Preheat the oven to 180ºC/350ºF/gas 4. Snap the chocolate into a large heatproof bowl, add the butter and melt over a pan of gently simmering water, stirring regularly and making sure the water doesn't touch the base of the bowl, then leave to cool slightly.
Separate the eggs, putting the yolks into the bowl of a free-standing mixer with the caster sugar, or into a large bowl if using an electric hand whisk. Whisk for 2 minutes, or until pale and fluffy, then stir in the melted chocolate.⏱ 2 min
Whisk the egg whites and a pinch of sea salt in a separate bowl until stiff, using the free-standing mixer or electric hand whisk. Working in batches, gently fold them into the chocolate mixture, then sift and fold in the cocoa.
Depending on your chosen recipe in Simply Jamie, either pour the cake batter directly into a greased 25cm x 30cm roasting tray, or spread evenly across a 30cm x 40cm greaseproof-paper-lined baking tray.
Bake for 15 minutes exactly – until just springy to the touch and gooey in the middle. Remove from the oven, and follow the rest of your recipe, like Chocolate tiramisù.⏱ 15 min