Chocolate, Hazelnut and Sea Salt Tart

Some puddings are for sharing and some are for staring at. This tart is both. A dark cocoa pastry, shot through with toasted hazelnuts, holds a ganache so glossy you can almost see your reflection in it, and the whole thing is finished with crunched hazelnuts and a deliberate scatter of flaky salt. It is not a difficult tart, but it is a slow one, built in stages with a long sit at the end, and the reward is a slice that tastes like the best chocolate you have ever eaten somehow improved. The clever twist is sea salt, which does not make the tart taste salty so much as make the chocolate taste more profoundly of itself.

Chocolate and hazelnut, an old romance

The pairing of chocolate and hazelnut is so familiar now, thanks largely to a certain jar of spread, that it is easy to forget it was born of necessity. In Piedmont in northern Italy, chocolatiers in the early nineteenth century faced cocoa shortages and rising prices — sharpened, in the 1860s, by the Napoleonic blockades that had earlier choked the supply of cacao into the region. They stretched their precious chocolate by blending it with the region’s abundant Tonda Gentile hazelnuts, the small, round, intensely flavoured variety grown in the Langhe hills around Alba. The result was gianduja, a smooth chocolate-hazelnut confection named, so the story goes, after Gianduja, a masked carnival character from Turin. It became the pride of the city and, much later, the ancestor of every chocolate-hazelnut product on the supermarket shelf. What began as a thrifty workaround turned out to be a genuine improvement, because hazelnut’s warm, roasted sweetness rounds chocolate’s bitterness in a way few other flavours manage.

This tart leans on that history. The hazelnuts appear twice, ground into the pastry and toasted on top, so their flavour frames the chocolate from both sides. It is gianduja reimagined as a sliceable centrepiece.

Toasting is not an optional nicety with hazelnuts, it is the whole point of using them. Raw hazelnuts taste flat and faintly grassy; a few minutes in a dry pan or a hot oven triggers the Maillard reaction, the same browning chemistry that gives roasted coffee and seared meat their depth, and the nut’s flavour swings round to something warm, buttery and unmistakably roasted. Toasting also drives off moisture, which is why toasted nuts grind to a finer, drier powder that folds cleanly into pastry rather than clumping into a paste. If you buy blanched hazelnuts with the skins already removed you save a step, but if yours still have their papery skins, rub them in a clean tea towel while warm and most will flake away; a few stubborn flecks do no harm.

Building the tart, stage by stage

Start with the pastry. Toast 60g blanched hazelnuts in a dry pan over a medium heat for 4 to 5 minutes until fragrant and golden, cool them, then blitz to a fine powder. Pulse 200g plain flour, 30g cocoa, 80g icing sugar, a quarter-teaspoon of fine salt, the ground hazelnuts and 140g cold diced butter to fine crumbs. Add 1 egg yolk and 2 to 3 tablespoons of ice-cold water, just enough to bring the dough together. Shape into a disc, wrap and chill for at least an hour.

Roll the pastry out and line a 23cm loose-bottomed tart tin, pressing well into the corners. Trim the edges and chill for 20 minutes while the oven heats to 170C fan. Line with greaseproof paper and baking beans, blind bake for 15 minutes, then remove the paper and beans and bake for a further 8 to 10 minutes until the base is dry. Cool completely.

For the ganache, heat 300ml double cream until just steaming, pour it over 300g chopped dark chocolate and leave it for two minutes. Stir gently from the centre outwards until smooth and glossy, then stir in 40g softened butter and 1 tablespoon honey. Pour into the cooled case, tap the tin to settle and level it, and leave to set at room temperature for at least three hours. Just before serving, scatter with 2 tablespoons chopped toasted hazelnuts and a generous pinch of flaky sea salt.

Why the technique matters

There are three jobs here and none is hard, but each needs care. The pastry is enriched with ground toasted hazelnuts and cocoa, which makes it more fragile than a plain shortcrust, so chill it well and patch any cracks with offcuts rather than fretting. Blind bake it fully, because there is no further baking once the ganache goes in; an undercooked base is the one thing that will let this tart down.

The ganache is just cream and good dark chocolate, but technique matters. Heat the cream until it steams rather than boils, pour it over the chopped chocolate, and then leave it alone for a couple of minutes before stirring from the centre outwards. Beating air in or stirring too soon gives a dull, grainy result; patient stirring from the middle draws the melted chocolate and cream into a stable emulsion and gives a mirror. A little butter and a spoon of honey added at the end bring extra shine and a softer, more luxurious set, because the honey’s invert sugars keep the ganache from setting hard. Pour it into the cooled case and then, crucially, leave it at room temperature to set rather than rushing it into the fridge, which can dull the surface and firm the ganache to an unpleasantly hard chill.

If the ganache ever “splits” — turns oily and grainy rather than glossy — it has broken, usually because the cream was too hot or the chocolate too cold. Rescue it by whisking in a tablespoon of cold milk or cream a little at a time until it comes back together into a smooth emulsion. It is the same principle behind the dark chocolate mousse with espresso and flaky salt: dark chocolate and salt were made for each other.

The salt itself deserves a word, because it is doing real work rather than sitting there for show. Chocolate is naturally bitter, and our tongues register bitterness strongly; a small amount of salt suppresses that bitter perception and, at the same time, makes the sweet and roasted notes read louder, which is why a scatter of flakes makes the whole tart taste more intensely of chocolate rather than of salt. Use a flaky sea salt such as Maldon rather than fine table salt: the large, brittle crystals sit on the surface and dissolve slowly, so you get bright little pinpricks of contrast in a mouthful rather than an even, background saltiness. Scatter it on only just before serving, because left overnight the crystals draw moisture from the ganache, soften and disappear into the surface.

Tips, substitutions and getting ahead

Use the best dark chocolate you can, ideally around 70 per cent cocoa, because it is the entire flavour of the filling. Anything much sweeter will make the tart cloying; anything much darker can turn bitter once it sets. If your kitchen is very warm in high summer, the ganache may need a short spell in the fridge to firm up, but bring the tart back to cool room temperature before serving so the filling is silky rather than solid.

Both elements can be made ahead. The baked pastry case keeps in an airtight tin for a couple of days, and the finished tart is happy for two days under a cake dome, the flavour deepening overnight. Add the hazelnuts and salt only just before serving so they stay crunchy and the salt does not dissolve into the surface. Cut it with a hot, dry knife, wiped between slices, for clean edges.

Toasted almonds or pecans stand in nicely for the hazelnuts if that is what you have, and a splash of espresso in the warm cream deepens the chocolate further without reading as coffee. A tablespoon of a hazelnut liqueur such as Frangelico, or a little dark rum, stirred into the finished ganache is another good route if the tart is strictly for the grown-ups. The pastry is the only part that takes real care, so a final word on it. Because it is enriched with ground nuts and cocoa, it has less stretch than ordinary shortcrust and will crack rather than drape if you rush it. Roll it between two sheets of greaseproof paper to save flouring and tearing, and if it does split as you line the tin, simply press the pieces together and patch any holes with offcuts; nobody will know once the ganache is poured. Chilling the lined case before baking sets the butter and stops the sides slumping. A small slice of this tart goes a long way, so a single one genuinely serves a crowd, and a spoonful of crème fraîche or a few fresh raspberries alongside cuts the richness beautifully if anyone needs rescuing. If you love that dark-chocolate-and-salt register, the rye chocolate chip cookies with smoked salt chase the same idea in a form you can eat standing at the counter.