Coffee tres leches cake

Heat the oven to 350 with a rack in the centre.

Separate the eggs, whites into the stand mixer bowl and yolks aside; no yolk may get into the whites.

Lay greased parchment strips along the edges of an ungreased 13 by 9 pan; an ungreased pan gives the batter friction to climb, a non-stick one is too slick.

Set a baking core in the centre of the pan if using.

Whip the whites with half the sugar, the cream of tartar and the salt on medium until frothy, then medium-high to firm, straight-standing stiff peaks that hold the marks of the whisk — no further, or they go dry and grainy.

Scrape the whites into a wide bowl and return the whisk and bowl to the mixer for the yolks.

Beat the yolks with the rest of the sugar on high about three minutes until pale, light and ribboning — the mixture sits on top of itself for a few seconds before settling.

Stream in the melted, cooled butter slowly to emulsify, then the vanilla.

Sift the flour over the yolks through a mesh strainer and mix on low to incorporate.

Fold a quarter to a third of the whites into the yolks to lighten them, scrape the whole thing into the bowl of whites and fold until even with no streaks, working quickly because egg white foam destabilises against fat.

Pour into the pan, smooth to a single layer and tap sharply on the counter to pop the large bubbles.

Bake 25 to 30 minutes until domed and deep golden brown across the surface; 27 minutes here.

For the soak, combine the whole milk, heavy cream, the full can of sweetened condensed milk, vanilla, a pinch of salt and the coffee and whisk until the condensed milk dissolves.

Invert the sponge onto a cooling rack straight out of the oven and cool it upside down, so it releases steam without collapsing.

Cut around the sides, peel the film off the surface to expose the crumb, and unmold.

Line the cleaned pan with plastic, return the sponge and poke holes all over to make channels for the soak.

Pour the soak over, cover with plastic and refrigerate 24 hours; a plate on top keeps the sponge submerged.

Whip the mascarpone, heavy cream and vanilla paste to softly whipped, just past pourable — mascarpone stiffens further as it sits. It is not sweetened.

Lift the cake out by the plastic, pouring off excess soak if there is more than wanted.

Scrape the whipped mascarpone over the top and grate bar chocolate over it. Serve cold, spooning a little of the excess soak onto the plate as a sauce.