Preheat and prepare. Preheat your oven to 200°C (180°C fan) and line a 12-hole muffin tin with paper cases. The oven needs to be hot to give those muffins a good initial lift.

Whisk the dry ingredients. In a large bowl, sift together the flour, cocoa powder, sugar, baking powder, bicarbonate of soda, and salt. Whisk them thoroughly until the mixture is a uniform, dark brown colour and feels light and airy when you lift the whisk. You should see no lumps of cocoa.

Combine the wet ingredients. In a separate jug or medium bowl, whisk the eggs until they are frothy and pale yellow. Add the buttermilk, vegetable oil, and vanilla extract. Whisk again until everything is fully combined and looks like a single, glossy liquid.

Mix the batter (do not overmix). Pour the wet ingredients into the bowl of dry ingredients. Using a rubber spatula, fold the mixture together gently. Stop as soon as you see the last streak of flour disappear. The batter will look lumpy and slightly thick—this is exactly what you want. Overmixing at this stage will develop the gluten and make your muffins tough.

Fold in the chocolate. Add the chopped dark chocolate and the milk chocolate chips to the batter. Fold them in with just two or three turns of the spatula. You want the chocolate evenly distributed, but the batter should still look slightly irregular.

Rest the batter (crucial step). Cover the bowl with a clean tea towel and let the batter rest at room temperature for 15 minutes. During this time, the starch in the flour will absorb the liquid, which helps create a higher, domed top. You will notice the batter thickening slightly.

Fill the cases. Use a large ice cream scoop or two spoons to divide the batter evenly among the 12 paper cases. Fill each case right to the top—almost overflowing. The batter will be quite stiff and mounded. This is the secret to a tall, bakery-style muffin.

Bake until domed and fragrant. Place the tin in the preheated oven and bake for 18–22 minutes. At the 10-minute mark, the kitchen will begin to smell deeply of chocolate. The muffins are ready when the tops are firm to a gentle touch and spring back, and a skewer inserted into the centre comes out with a few moist crumbs (not wet batter). The edges will have pulled away slightly from the paper cases.

Cool in the tin. Remove the tin from the oven and let the muffins cool in the tin for 5 minutes. This allows the structure to set. The aroma at this point is absolutely intoxicating—rich, sweet, and deeply comforting.

Transfer to a wire rack. After 5 minutes, carefully lift the muffins out of the tin and place them on a wire rack to cool completely. If you try to move them immediately, they will be too fragile and might crumble.