Jon's Shortbread Creams

STEP 1: MAKE THE SALTED BUTTERSCOTCH

Start here, because it must be completely cold before it meets the buttercream. Melt the butter and dark brown sugar together in a small heavy saucepan over medium heat, stirring, until the sugar has fully dissolved and the mixture is smooth. Let it bubble for 3-4 minutes without stirring, until it darkens and smells of toffee. Off the heat, stand back and pour in the double cream; it will hiss and rise. Whisk smooth, return to the heat and boil for 1-2 minutes until glossy and slightly thickened (about 112C / 234F on a thermometer). Off the heat, beat in the fine sea salt and vanilla extract. Taste it: it should read as unmistakably salted, because the sweetness of the buttercream will mute it. Pour into a shallow bowl and cool to room temperature, about 1 hour.

STEP 2: MAKE THE SHORTBREAD DOUGH

Beat the softened butter with the caster sugar, light muscovado sugar and fine sea salt until pale and creamy, 2-3 minutes. Sift in the plain flour, wholemeal flour and rice flour if using, then mix on low just until the dough gathers into clumps; stop the moment it comes together. Overworking develops gluten and gives a tough, bready biscuit instead of a short one. Bring it together by hand into a smooth block.

STEP 3: SHAPE THE SHELLS

Divide the dough into 24 pieces of 20 g each, weighing every one. This is the step that makes the bake time honest. Roll each piece into a ball. Lightly flour the inside of a scallop shell or a madeleine hollow, press a ball firmly in, and work the dough out to the edges so the ridges take a clean impression. Turn the shell over, ease the biscuit out with the tip of a knife, and press it gently onto the lined baking sheet so it sits at an even 7 mm, flattening any dome at the centre. Space them 3 cm apart and repeat. Dust very lightly with caster sugar if you like a faint crackle on the surface.

STEP 4: CHILL THE SHAPED BISCUITS

Refrigerate the trays for at least 30 minutes, until the biscuits are firm to the touch. A butter-heavy dough that goes into the oven soft will spread, thin unevenly and brown unpredictably. Meanwhile, heat the oven to 160C conventional / 145C fan / 325F.

STEP 5: BAKE TO COLOUR

Bake for 20-24 minutes, rotating the trays at the 14-minute mark. Ignore the clock at the end and read the biscuits instead: the edges should be a definite deep gold, the faces evenly golden rather than blond, and the surface dry and sandy-looking with no damp sheen at the centre. A biscuit lifted from the sheet should feel firm all the way through, not just at the rim. If the centres are still pale, give them another three or four minutes and check again. Aberffraw shortbread that looks correct at 16 minutes is underbaked; in a dough this plain the colour is the flavour. They will still be slightly soft when hot and will crisp as they cool.

STEP 6: COOL COMPLETELY

Leave the biscuits on the sheets for 5 minutes to firm up, then transfer them to a wire rack and cool completely, at least 45 minutes. They must be stone cold before filling, or the butterscotch cream will slump and the shells will soften.

STEP 7: WHIP THE BUTTERSCOTCH CREAM

Beat the softened butter on its own for 2 minutes until very pale and light. Add the sifted icing sugar in two additions, beating well between them. Add all the cooled butterscotch and beat for a further 2-3 minutes until smooth, glossy and mousse-like. If it looks loose, chill for 10 minutes and re-whip; if it is stiff, beat in a teaspoon of cream. Taste again for salt.

STEP 8: FILL AND ASSEMBLE

Turn half the shells ridge-side down. Pipe or spread a generous 3 teaspoons of cream onto each, stopping 5 mm short of the edge. Top with a second shell, ridge-side up, and press gently and evenly until the filling just reaches the rim; do not squeeze it out. Scatter a few flakes of sea salt on the exposed filling edge if you like.

STEP 9: REST AND SERVE

Rest the assembled creams for 30 minutes at cool room temperature to let the filling set. They are at their best on the day they are made, while the shells still snap and the filling is soft. Store unfilled shells airtight for up to 5 days and assemble on the day.