Make the vanilla custard base: In a medium saucepan, whisk together the caster sugar, cornflour, and a pinch of salt. The mixture should look pale and powdery, with no lumps visible. Crack the eggs into the saucepan and whisk until the mixture turns a light lemon yellow and feels smooth against the whisk.

Add the milk slowly: Pour in the whole milk in a steady stream while whisking constantly. You’ll see the mixture turn pale and thin as the milk incorporates. Keep whisking until the liquid is completely uniform — no streaks of egg yolk remaining.

Cook the custard: Place the saucepan over a medium heat. Stir continuously with a wooden spoon or silicone spatula, scraping the bottom and sides. After about 4-5 minutes, you’ll feel the mixture start to thicken, and wisps of steam will rise from the surface. When it begins to bubble gently — you’ll hear a soft popping sound — cook for one more minute. The custard should be thick enough to coat the back of the spoon, and when you run a finger through it, the line should hold clearly.

Finish the custard: Remove the saucepan from the heat. Stir in the butter until it melts completely — you’ll see the custard take on a glossy sheen. Add the alcohol-free vanilla extract and stir until the fragrance fills the air. Pour the custard into a wide, shallow bowl to cool for 10 minutes. Cover with cling film pressed directly onto the surface to prevent a skin from forming.

Slice the bananas: While the custard cools, peel the bananas and slice them into 1 cm rounds. They should look firm and bright yellow, with no browning yet. If your bananas are very ripe, handle them gently so they don’t turn mushy.

Whip the cream: In a large bowl, pour the double cream and add the icing sugar. Using a hand whisk or electric mixer, whip until soft peaks form. When you lift the whisk, the cream should hold a soft droop that doesn't collapse immediately. The texture should be airy and cloud-like.

Layer the pudding: In a 2-litre serving dish (or individual glasses), spread a thin layer of custard across the bottom. Arrange a single layer of vanilla wafers over the custard — you’ll hear a faint click as they settle. Top with a layer of banana slices, then a third of the remaining custard. Repeat the layers: wafers, bananas, custard, until you’ve used all ingredients. Finish with a final layer of custard on top.

Top with cream and chill: Spread the whipped cream evenly over the top layer of custard. You can create swirls with the back of a spoon for a decorative finish. Cover the dish loosely with cling film and refrigerate for at least 2 hours. The wafers will soften as they absorb the custard, creating that classic cake-like texture. When ready to serve, the top should feel cool and firm to the touch.