Preheat and prepare your tin: Set your oven to 180°C (fan-assisted). Line a 12-hole muffin tin with paper cases — the paper should feel crisp to the touch when the oven is ready. This ensures the muffins will bake evenly from the start.

Mash the bananas: In a large mixing bowl, mash the bananas with a fork until you have a lumpy purée. You want some small chunks remaining — about the size of peas — so the muffins have lovely pockets of soft banana. The mixture should smell intensely sweet and fruity.

Combine wet ingredients: Pour in the melted butter, caster sugar, egg, and vanilla extract. Stir vigorously with the same fork until everything is well combined. The batter will look glossy and smell richly of vanilla and banana. If it seems very thick, add the milk now and stir until it loosens slightly.

Sift and fold dry ingredients: Sift the plain flour, bicarbonate of soda, baking powder, and salt directly over the wet mixture. Use a spatula to fold gently — just 10 to 12 strokes. Stop when you see no more streaks of white flour. The batter should look slightly lumpy, not smooth; overmixing will make the muffins tough.

Add the chocolate chips: Tip the dark chocolate chips into the bowl and fold them through with three or four gentle turns. You should see the chips evenly distributed, with dark flecks against the pale batter. The batter will now smell deeply of chocolate and banana.

Fill the muffin cases: Divide the batter evenly among the 12 paper cases. Each case should be about three-quarters full — the batter will feel heavy and sticky as you spoon it. For a bakery-style dome, use two spoons to drop the batter into the centre of each case rather than spreading it.

Bake until golden: Place the tin in the centre of the oven and bake for 18-20 minutes. At 18 minutes, insert a skewer into the centre of a muffin; it should come out with a few moist crumbs attached, not wet batter. The tops will be domed, golden brown, and the kitchen will smell like a bakery.

Cool correctly: Remove the tin from the oven and let it sit on a wire rack for 5 minutes. The muffins will be very hot and fragile. After 5 minutes, lift each muffin out of the tin and place it directly on the wire rack to cool completely. You should hear a slight crackle from the tops as they cool — that's the sugar crust forming.