Millionaire's shortbread

Cream the cool room temperature butter with the sugar by hand with a spatula; a hand or stand mixer is not necessary.

Work in the kosher salt until the sugar is incorporated and the mixture is a little fluffy and pale, a couple of minutes.

Stir in the vanilla extract.

Add the flour, working gently at first, until it forms big wet crumbs; preheat the oven to 350F.

Finish by hand with the fingertips, tossing and feeling for pockets of butter, which would melt and leave voids. Stop once there are no dry floury spots.

Grease the pan lightly with the butter wrapper and line it with parchment, only so the slab can be lifted out whole.

Scatter the crumbs evenly over the base and pat down with palms and fingertips, then compact with the flat bottom of a one cup measure. Flour the cup if it sticks.

Dock the shortbread all over with a fork, going right through to the bottom: it encourages evaporation and prevents puffing.

Bake on the centre rack at 350F about 20 to 25 minutes, to a medium golden brown all over. Too pale and it stays moist and soft under the caramel; too dark and it dries out and cracks when cut.

Tamp down any puffed areas very gently with the same measuring cup and let the base cool before the caramel goes on, so the shortbread can release its steam.

Put the Demerara sugar, butter, corn syrup, heavy cream, kosher salt, condensed milk, the vanilla seeds and the scraped pod into the saucepan.

Warm over medium, stirring well to dissolve the sugar, then raise to medium high to reach a rapid boil; after a minute or two drop back to medium.

Cook slowly to 240F, stirring constantly, standing over it the whole time. Low and slow gives even cooking, better browning and a caramel colour rather than a pale one, and stops it catching on the bottom.

Pluck out the vanilla pod and pour the caramel over the shortbread, scraping the sides but not the very bottom of the pan, which is hotter and leaves hardened pockets.

Spread wall to wall into an even layer before it sets.

Cool about 20 minutes at room temperature, then chill in the fridge until cold.

Melt the chocolate in a bowl over about an inch of water that is not boiling rapidly and not touching the bowl; keep all water out of the bowl or the chocolate seizes. Take it off at about 98 percent melted and let carryover finish it.

Dry the bottom of the bowl, scrape the chocolate over the cold caramel and spread it fast, into a thin even layer.

Sprinkle flaky salt over before the chocolate hardens. Cocoa nibs or chopped nuts would also work.

Leave at room temperature until the chocolate is fully set, a few minutes in the fridge if needed.

Lift out by the parchment, loosening the unlined sides with an offset spatula; trim all four sides and cut small, halving and halving again, wiping the knife under hot water and drying it between cuts.