Breton Shortbread Cake with Salted Caramel

Make the caramel filling: spread the 120 g caster sugar in an even layer in a light-coloured heavy saucepan — do not stir. Place a sheet of baking paper on a heatproof surface nearby.

Cook the sugar over medium heat until the edges begin to melt and turn amber, then gently swirl the pan — never stir — until all the sugar has dissolved and the caramel is a deep mahogany colour (175–180°C on a sugar thermometer).

Remove the pan from the heat and immediately pour in the warmed double cream in a slow stream, whisking constantly — the mixture will bubble violently. Whisk in the salted butter cubes one at a time until fully incorporated, then stir in the crème fraîche and ½ tsp fleur de sel.

Pour the caramel onto the prepared baking paper, spread to a rough 18 cm disc and leave to cool completely at room temperature until it is firm enough to handle but still pliable, approximately 1 hour.

Grease a 20 cm round cake tin (or four individual 10 cm tart rings) with butter and line the base with baking paper.

Beat the 150 g softened unsalted butter and 100 g caster sugar together with a wooden spoon or stand mixer on medium speed until pale and fluffy, about 3 minutes.

Beat in 2 of the egg yolks and the vanilla extract until fully combined, then sift in both flours and the 1 tsp fleur de sel and fold together to form a soft, cohesive dough.

Divide the dough into two equal portions. Press one portion evenly across the base of the prepared tin to a uniform thickness of about 8 mm.

Lay the set caramel disc over the dough base, leaving a 1 cm border clear all the way around the edge.

Press the remaining dough out between two sheets of baking paper to a matching disc, then carefully lay it over the caramel and press the edges together firmly to seal completely.

Beat the reserved third egg yolk with 1 tsp cold water and brush the surface evenly. Refrigerate the tin, uncovered, for 30 minutes.

Use a fork to score a classic crosshatch pattern across the chilled surface, then scatter a final pinch of fleur de sel over the top.

Bake in an oven preheated to 170°C fan (190°C conventional) for 35–40 minutes until the surface is a deep, even golden brown and the edges have pulled away slightly from the tin.

Leave to cool in the tin for 15 minutes, then turn out onto a wire rack and cool for at least 1 hour before slicing — the caramel must set or it will spill.