Preheat and Prep: First, preheat your oven to 180°C (160°C fan). Grease and line a 23cm (9-inch) square baking tin with parchment paper, leaving some overhang to help lift the brookies out later.

Make the Brownie Batter Base: Place the chopped dark chocolate and cubed butter in a heatproof bowl set over a saucepan of simmering water (a bain-marie). Stir occasionally until melted and smooth. You can learn more about the best ways for melting chocolate here. Remove from the heat and set aside to cool slightly for about 10 minutes.

Combine Wet Brownie Ingredients: In a separate large bowl, whisk the eggs, caster sugar, and vanilla extract together for 2-3 minutes until the mixture is pale and has thickened slightly.

Finish the Brownie Batter: Pour the cooled chocolate-butter mixture into the egg mixture and gently fold to combine. Sift the plain flour, cocoa powder, and salt over the wet ingredients and fold everything together with a spatula until just combined. Be careful not to overmix.

Layer the Brownie Batter: Pour the brownie batter into your prepared tin and spread it out evenly with your spatula. Set aside while you make the cookie dough.

Make the Cookie Dough: In a large bowl (you can use a stand mixer with the paddle attachment or an electric hand mixer), beat the softened butter with the light brown sugar and caster sugar until light and fluffy, about 3-4 minutes.

Finish the Cookie Dough: Beat in the egg and vanilla extract until well combined. In a separate bowl, whisk together the plain flour, bicarbonate of soda, and salt. Add the dry ingredients to the wet ingredients and mix on a low speed until just combined. Finally, stir in the chocolate chips.

Assemble the Brookies: Take spoonfuls of the cookie dough and dot them all over the surface of the brownie batter. What works best for me is using a small ice cream scoop for even portions. Don't press the dough down; just let it sit on top.

Bake to Perfection: Bake for 25-30 minutes. The cookie dough should be golden brown, and the brownie layer should be set at the edges. A skewer inserted into the centre should come out with moist, fudgy crumbs attached, not completely clean.

Cool Completely: Let the brookies cool completely in the tin on a wire rack. This is a crucial step! Cutting them while warm will be a messy affair. Once cool, use the parchment paper overhang to lift them out and cut them into 16 squares.