Flourless chocolate cake

Melt the butter and chocolate together very gently for about five minutes over the lowest possible heat.

Separate six eggs, scooping the yolk from hand to hand rather than passing it between the shell halves.

Whisk the whites by hand until they hold a soft peak, about eight minutes.

Add the sugar, vanilla, salt, cornstarch, instant coffee and buttermilk to the yolks.

Scrape the melted chocolate into the yolks, warm enough to pour but not hot enough to cook them, and whisk until combined.

Gently fold the whipped whites into the chocolate with a spatula; the air in the whites does the leavening.

Line a nine-inch springform with parchment, spray the sides, pour in the batter and tap it level.

Set the springform on a sheet tray and bake at 275F for 60 to 70 minutes until fully set.

Cool at least one hour, preferably two, then release the collar.

Dust the top lightly with cocoa powder through a fine mesh strainer.