Heat the oven and line your tin. Set the oven to 175°C (155°C fan). Line a 900 g loaf tin with a strip of parchment paper that overhangs the two long sides — this becomes a handle later. There is no need to grease underneath it.

Mash the bananas first. In your largest mixing bowl, mash the bananas with a fork until you have a lumpy purée. You want some texture left, not a smooth liquid — those little pockets of banana keep the crumb tender. It should smell sweet and slightly fermented, like overripe fruit.

Whisk in the wet ingredients. Add the melted butter, brown sugar, eggs, vanilla and yogurt. Whisk for about 30 seconds until the mixture is glossy and uniform in colour, with no streaks of egg white visible. It will look slightly curdled at first, then come together.

Sprinkle, then stir. Scatter the bicarbonate of soda, salt, cinnamon and nutmeg directly over the surface, then stir them in with a spatula. This stops the raising agent from clumping in one spot. Add the flour and fold gently — about 12 to 15 strokes — until you can no longer see dry flour. Stop while the batter still looks a little rough.

Fold through the chocolate chips. Reserve a small handful for the top, then fold the rest in with three or four turns. The batter should be thick enough to hold a spoon upright for a second before it slumps back.

Fill and top the tin. Scrape everything into the lined tin and level the surface with the back of your spatula. Scatter the reserved chocolate chips and the demerara sugar across the top — the sugar gives you a crackly, caramelised lid.

Bake until deeply golden. Bake on the middle shelf for 55 to 65 minutes. At the 40-minute mark, check it: if the top is browning faster than you would like, tent it loosely with foil. It is ready when a skewer inserted into the centre comes out with a few moist crumbs but no wet batter, and the kitchen smells of caramelised banana and toasted chocolate.

Cool before slicing. Leave it in the tin for 15 minutes — it is still setting inside — then lift it out using the parchment handles and transfer it to a wire rack. Wait at least 30 minutes before cutting. I know that is the hardest part, but a hot slice will crumble in your hand.