Preheat the oven to 180°C (160°C fan). Line your mini muffin tin with paper cases. The paper cases stop the chocolate mixture from sticking and make for easy removal later.

Melt the chocolate and butter together. Place the chopped dark chocolate and cubed butter in a heatproof bowl set over a saucepan of gently simmering water. Stir occasionally with a wooden spoon. You’ll know it’s ready when the mixture is glossy, smooth, and falls off the spoon in a thick ribbon.

Whisk the eggs and sugar. In a separate large bowl, whisk the eggs, golden caster sugar, and vanilla extract together until pale and frothy. The mixture should look like a light caramel colour and leave a ribbon trail on the surface when you lift the whisk.

Combine the chocolate mixture with the eggs. Pour the melted chocolate and butter into the egg mixture, stirring gently with a spatula. The batter will darken immediately and smell deeply of rich chocolate. Keep stirring until no streaks remain.

Fold in the dry ingredients. Sift the plain flour, cocoa powder, and fine sea salt over the batter. Fold gently until just combined — you want to see a few floury streaks remaining before adding the nuts.

Add the nuts and chocolate chips. Tip in the toasted chopped nuts and milk chocolate chips. Fold two or three times until evenly distributed. The batter will be thick, glossy, and studded with crunchy bits.

Fill the mini muffin cases. Using a small spoon or a cookie scoop, divide the batter evenly among the 12 cases. Each case should be about three-quarters full. The tops should look slightly domed and uneven.

Bake for 10–12 minutes. Place the tin in the preheated oven. After 10 minutes, check the edges — they should look set and slightly cracked, while the centre still wobbles slightly when you gently shake the tin. The kitchen will smell like a chocolate shop.

Cool in the tin for 5 minutes. Remove the tin from the oven and place it on a cooling rack. Let the desserts sit for 5 minutes — this allows them to finish setting without drying out. The tops will sink slightly, creating a fudgy centre.

Transfer to a cooling rack and finish. Carefully lift each mini dessert out of the tin and place on the cooling rack. While still warm, sprinkle with a tiny pinch of flaky sea salt if using. Let them cool completely before serving, or enjoy warm for a gooey texture.