S'mores tart

Turn the oven on to 350 to bake the crust.

Melt the butter in a saucepan, which will be used again for the ganache.

Crush the graham crackers in a resealable bag with a rolling pin, lifting and shaking the bag so the largest pieces rise, then re-crushing until finely and uniformly ground. Do not use a food processor, which grinds too fine and makes the crust dense and greasy.

Add the kosher salt and the sugar to the crumbs.

Scrape in the five tablespoons of melted butter and add the egg yolk, mixing until it looks like wet sand and holds together when squeezed.

Rub the mixture between your palms so there are no clumps or dry patches.

Scatter about half the crumbs into the pan and press them against the sides with a straight sided one cup measure held parallel, leaving the top edge a little looser.

Press the rest into the bottom with the palm and smooth with the measuring cup, pushing a little up the sides.

Bake on a sheet tray until fragrant with a darkened edge, right around 15 minutes, in a range of 13 to 18.

Pour three quarters of a cup of the heavy cream into the saucepan and return the remaining half cup to the fridge to stay cold for whipping.

Warm the cream over medium heat until barely bubbling at the sides and steaming, not quite boiling.

Put the chopped chocolate in a large bowl with a pinch of salt and the four tablespoons of butter.

Let the cream cool 20 to 30 seconds so it does not shock the chocolate, then pour it over and make sure the chocolate is submerged; let sit a few minutes.

Cool the baked crust on a rack; the filling must not go into a hot crust.

If the ganache has not fully melted, rewarm it gently over a double boiler or in 10 second microwave bursts, stirring between, stopping before the chocolate is fully melted and letting carryover finish it.

If the ganache breaks, with beads of fat collecting on top, whisk in two tablespoons of cool tap water vigorously to bring it back.

Whip the reserved half cup of cold cream with a hand mixer to soft peaks that hold the marks of the whisk, and set aside.

Without washing the beaters, beat the room temperature ganache until it looks like chocolate pudding, thickened and holding the marks but still glossy.

Fold the softly whipped cream into the ganache gently until streak free.

Scrape into the cooled crust and spread into an even layer to the edge; let it set about 15 minutes.

Sprinkle the gelatin over a quarter cup of very cold tap water from a height and do not stir; let it hydrate about 10 minutes until firm and bouncy.

Bring water to just below a simmer for a double boiler and set a heatproof bowl on top without the bottom touching the water.

Melt the gelatin on its own in the bowl, stirring gently until completely liquid, without letting it boil.

Off the heat, add a pinch of salt, the corn syrup and the sugar, in that order, to cool the mixture before the egg whites go in.

Add the egg whites and half a teaspoon of the vinegar, return to the double boiler and whisk constantly until the sugar dissolves and the mixture is opaque, whitish and sticky; above 160 the whites are pasteurized.

Test by rubbing a dab between the fingertips: it should be smooth with no grit.

With clean grease free beaters, whip on low increasing to high into a meringue, adding the vanilla toward the end.

Keep beating on high until it holds tall peaks; with a hand mixer this took a solid 12 minutes.

Scrape the marshmallow onto the chocolate filling and make texture in the surface with a spoon.

Let the topping set at cool room temperature, ideally a couple of hours, for a clean slice.

Torch the marshmallow, keeping the flame moving because meringue toasts very quickly. Do not use the broiler, which burns the crust edge.

Let the marshmallow cool, release the tart from the ring and slice, wiping the knife between cuts.