Line a 20x30cm baking dish with baking parchment, and grease the sides with butter.

Melt the butter in a small saucepan over a medium-low heat to make beurre noisette. Wait for it to foam and separate into liquid and solids, and remove from the heat as soon as the solids start to turn a nutty brown. The butter should have a nutty scent to it. Carefully pour it immediately into a bowl to cool. Stir in the tahini, to allow it to melt into the warm butter and infuse.

Heat your oven to 170°C. Using an electric hand whisk, whisk the eggs, sugar and some grated vanilla bean together until light and creamy. Beat in the butter and tahini mixture until evenly combined.

Using a hand whisk, combine the flour, baking powder and salt in a bowl to ensure even distribution of the raising agent, and then fold it into the butter mixture, followed by the marshmallows (and the chocolate chips, if using).

Spread the mixture into your dish and smooth it out on top. Sprinkle the top liberally with sesame seeds. Bake for 25-30 minutes – you want the mixture to be baked through, but still moist and gooey, so keep an eye on it. Allow it to cool in the dish. Once it has set, slice and serve. It will keep in the fridge in an airtight container for up to 4 days.