Make the chocolate sauce: Put the chocolate and butter into a glass bowl set over a saucepan of simmering water, so that the bowl doesn’t touch the hot water.
Make the pancakes: Mix together the flour, cocoa, baking powder, soda, salt and sugar. In another bowl, whisk the egg whites to firm peaks. In a third bowl, beat the egg yolks, milk, sour cream and melted butter. Fold the egg whites into the egg yolk mix, then fold in the dry ingredients.
Heat a non-stick pan on a medium heat. Ladle spoonfuls of the batter in and cook on a medium heat until the surface starts to dry and small bubbles appear. Carefully turn them over and cook for another minute, then put to one side while you use up the rest of the batter. It should make around 12 pancakes.
Make the marshmallow filling: Put the egg whites, cream of tartar and caster sugar into a stand mixer and whisk to firm peaks. Meanwhile, heat the golden syrup and remaining caster sugar in a small saucepan, until it reaches 120C. With the stand mixer running, slowly pour the hot syrup into the egg whites and whisk until light, fluffy and starting to cool. Put the marshmallow filling into a piping bag fitted with a 1cm round tip.
Assemble the s’mores pancake stack: Create stacks of pancakes sandwiched together with a generous layer of marshmallow filling, finishing with marshmallow on top of the stack. Use a blowtorch to gently caramelise the visible marshmallow layers, then load the top with crushed Graham crackers and warm chocolate sauce.