Preheat your oven to 200°C (180°C fan) and line a 12-hole muffin tin with paper cases. The high initial temperature helps create that lovely domed top. While the oven warms, gather your ingredients—this is the moment to slow down and breathe.

In a large mixing bowl, whisk together the flour, cocoa powder, baking powder, bicarbonate of soda, salt, and caster sugar. Watch the cocoa powder bloom into the air; that deep, slightly bitter scent is the first sign of good things to come. Make sure there are no lumps of flour or cocoa hiding at the bottom.

In a separate jug or bowl, combine the oil, eggs, buttermilk, and vanilla extract. Whisk them until they look pale and homogenous, a single, glossy liquid. The buttermilk will react with the bicarbonate of soda later to give the muffins a tender lift.

Pour the wet ingredients into the dry ingredients and stir with a wooden spoon or rubber spatula. Use a gentle hand here; stir only until you see the last streak of flour disappear. The batter will be thick and look slightly lumpy—that’s exactly right. Overmixing will make the muffins tough, and we want them soft as a cloud.

Fold in the dark chocolate chips, if using, and then add the 120g of peanut butter. Give the batter two or three folds to distribute the peanut butter in thick, uneven ribbons. You want to see distinct streaks of peanut butter; a fully homogeneous batter will lose that wonderful pocket of salty creaminess.

Divide the batter evenly among the 12 paper cases. Each case should be about three-quarters full. Use a small ice cream scoop or two spoons—it’s a little messy, but that’s part of the charm. The batter will feel dense and slightly sticky against the spoon.

Take the remaining 2 tablespoons of peanut butter and warm it in the microwave for 10 seconds. Drop a small dab on top of each muffin, then use a toothpick or the tip of a knife to swirl it gently into the surface. Don’t over-swirl; a few lazy figure-eights will do.

Bake for 18–22 minutes. At the 15-minute mark, your kitchen will smell like a patisserie crossed with a cosy diner. The muffins are done when they spring back lightly when pressed in the centre, and a skewer inserted comes out with a few moist crumbs (not wet batter). The tops should feel set and look crackled.

Let the muffins cool in the tin for 5 minutes. This rest is crucial—it lets the structure settle. Then transfer them to a wire cooling rack. Listen for the faint crackle of the dome as they cool; it’s a sound of success.