Hazelnut Mousse — a light praline mousse with caramelised hazelnuts

i. Origin & history

Hazelnuts have been grown and eaten in Europe since prehistory, but their great culinary home is Piedmont in north-western Italy and the neighbouring regions of France. The Piedmontese Tonda Gentile delle Langhe variety, prized for its round shape, easy peeling and intense aroma when roasted, is protected under the name Nocciola del Piemonte and is used by confectioners around the world.

Piedmont is also the birthplace of gianduja, the blend of chocolate and hazelnut paste developed by Turin confectioners in the nineteenth century. The story often told is that hazelnuts were used to stretch scarce cocoa during the Napoleonic era; whatever the exact origin, gianduja became the ancestor of every chocolate-hazelnut spread.

In France, the hazelnut's great contribution to pastry is praliné: hazelnuts (often mixed with almonds) cooked in caramel, cooled and ground until they release their oil and become a smooth, flowing paste. It became a pillar of French pâtisserie in the nineteenth and twentieth centuries, giving its flavour to the Paris-Brest, praline buttercreams, chocolates and countless entremets. A mousse made with it was a natural development, and mousse au praliné appears on French restaurant menus and as a layer in modern mousse cakes.

The hazelnut mousse is now part of the standard repertoire of French and Italian pastry, served in glasses as a plated dessert, piped into tartlets or set between layers of dacquoise and chocolate in layered cakes.

ii. How to fold oily praline into cream without collapsing it

Praline paste is around half nuts and half caramelised sugar, and the nuts contain a lot of oil. Fat is the enemy of whipped cream: stirred directly into whipped cream, the oil in praline paste can make the cream lose its air and turn heavy, greasy and sometimes grainy. The solution is to emulsify the praline into a warm, liquid base first, so it is evenly dispersed before it meets the cream.

Here, the base is a crème anglaise — milk, egg yolks and sugar cooked gently to about 82 °C, until it thickens and coats a spoon. Cooking the yolks makes the mousse safe without raw eggs and gives it a rich, custardy body. A little gelatine dissolved in the hot custard sets the mousse just enough to hold its shape. The praline paste is then blended into the warm custard, where the egg yolks' natural emulsifiers bind the nut oil into a smooth, glossy cream.

The custard is cooled to about 30 °C before the whipped cream goes in. At this temperature it is still fluid enough to fold smoothly, but cool enough not to melt the cream. Too warm and the mousse deflates; too cold and the gelatine begins to set, leaving lumps.

Finally, the cream is whipped only to soft peaks. It should still flow slightly, because folding thickens it further. Stiff cream is hard to incorporate evenly and gives a dense, buttery mousse.

iii. Ingredients

Makes 6 servings · scroll the side panel to adjust

• 150 ml whole milk
• 2 egg yolks
• 30 g caster sugar
• 4 g leaf gelatine (2 sheets)
• 150 g hazelnut praline paste
• 1 pinch flaky salt
• 300 ml double cream, well chilled
• 60 g blanched hazelnuts, to decorate
• 40 g caster sugar, for the caramelised hazelnuts

Praline paste is sold by specialist baking suppliers and some delicatessens; look for one with at least 50% nuts. You can make your own: caramelise 150 g toasted hazelnuts in 100 g sugar, cool, then blend in a strong food processor for several minutes until it turns into a smooth, runny paste (see hazelnut praline). Chocolate hazelnut spread is not a substitute — it is mostly sugar and vegetable oil and lacks the caramel depth. For a vegetarian mousse, replace the gelatine with ½ tsp agar-agar boiled in the milk.

iv. Method

1. Soak the gelatine in cold water for 5 minutes. Heat the milk until steaming.
2. Whisk the yolks and 30 g sugar, pour on the hot milk while whisking, then return to the pan. Cook over a low heat, stirring constantly, until the custard thickens slightly and coats the back of a spoon, about 82 °C. Do not let it boil.
3. Remove from the heat and stir in the squeezed gelatine until dissolved. Pour the hot custard over the praline paste and salt in a jug, and blend with a stick blender until completely smooth and glossy.
4. Cool, stirring occasionally, until it reaches about 30 °C — barely warm.
5. Whip the cream to soft peaks. Stir a third into the praline custard, then fold in the rest gently until even.
6. Divide between six glasses or ramekins and chill for at least 3 hours, until set.
7. For the decoration, toast the hazelnuts in a dry pan for 4–5 minutes, add 40 g sugar and stir over a medium heat until the sugar melts and coats the nuts in amber caramel. Tip onto baking paper, separate and cool, then roughly chop. Scatter over the mousses just before serving.

v. Tips & common mistakes

• Blend the praline into the custard. A stick blender gives a perfect emulsion; stirring alone can leave oily streaks.
• Watch the custard temperature. At 82 °C it thickens; much above 85 °C the yolks scramble. Strain it if in doubt.
• Cool before folding. A warm base melts the cream and the mousse turns soupy.
• Whip the cream softly. Soft peaks fold in smoothly and give a light, airy set.
• Add a pinch of salt. It sharpens the nutty, caramel flavour and stops the mousse tasting flatly sweet.
• Decorate at the last minute. Caramelised hazelnuts go sticky in the fridge; scatter them on just before serving.

vi. Variations

A gianduja mousse blends 50 g melted milk or dark chocolate into the praline custard for a chocolate-hazelnut flavour. An almond praline mousse uses almond praliné instead. Layer the mousse in a glass with coffee-soaked biscuit crumbs for a tiramisu-like dessert, or pipe it onto a crisp hazelnut dacquoise base with a layer of chocolate ganache for a simple entremets. A spoonful of hazelnut liqueur or a little espresso in the custard both work well.

For other praline desserts, see the Paris-Brest and the chocolate hazelnut tart. Other mousses on DessertCat include the white chocolate mousse and the orange mousse, and the Italian tartufo pairs hazelnut and chocolate in frozen form.

vii. Serving & storage

Serve the mousse chilled in small glasses, topped with caramelised hazelnuts and, if you like, a few shavings of dark chocolate or a crisp biscuit alongside. It is rich, so 100 ml portions are generous. It works well as a make-ahead dinner-party dessert and pairs well with espresso or a glass of sweet wine.

Keep the mousse covered in the fridge for up to 2 days. The caramelised hazelnuts keep for a week in an airtight jar at room temperature. The mousse can also be frozen for up to a month for a semifreddo-like dessert; serve it after 10 minutes at room temperature.

ix. More from French

• Hazelnut Praline — the mousse's foundation
• Paris-Brest — praline cream choux ring
• Hazelnut Meringue — crisp nut meringue
• White Chocolate Mousse — silky and pale
• Chocolate Hazelnut Tart — praliné and ganache
• Tartufo — Italian frozen truffle