Infuse the milk. Pour the milk into a medium saucepan. Scrape the seeds from the vanilla pod into the milk, then drop the pod in too. Place over a medium heat and bring it to a gentle simmer. You'll know it's ready when small bubbles appear around the edge of the pan and the milk smells beautifully fragrant. Do not let it boil. Remove from the heat, cover the pan, and let it steep for 15 minutes. This step is where the deep vanilla flavour begins.

Make the custard base. In a large bowl, whisk the egg yolks and caster sugar together until they turn a pale, creamy yellow and the mixture falls from the whisk in a thick ribbon. This will take about 2-3 minutes of steady whisking. Sift the cornflour and salt into the yolk mixture and whisk again until completely smooth, with no lumps.

Temper the eggs. Slowly pour a ladleful (about 100ml) of the warm, infused milk into the egg mixture, whisking constantly. This raises the temperature of the eggs gently so they don't scramble. Repeat with a second ladleful, still whisking. Then, pour the entire egg mixture back into the saucepan with the remaining milk, whisking all the while.

Cook the pudding. Place the saucepan over a medium-low heat and switch to a wooden spoon. Stir constantly, scraping the bottom and corners of the pan. You'll feel the mixture start to thicken after about 4-5 minutes. It will change from a thin liquid to a thick, glossy cream that plops rather than pours. The final cue is when you lift the spoon and the custard coats the back thickly; run your finger through it, and the line should hold. This is the 'nappe' stage. Remove from the heat immediately.

Finish the custard. Fish out the vanilla pod (rinse it and save it for making vanilla sugar). Add the softened butter and the 2 teaspoons of vanilla extract, stirring until the butter is completely melted and the custard is silky and glossy. Press a piece of cling film directly onto the surface of the custard to prevent a skin from forming. Let it cool at room temperature for 20 minutes, then refrigerate for at least 1 hour until completely cold.

Whip the cream and prepare the bananas. In a chilled bowl, pour the cold double cream and add the icing sugar. Whisk with an electric mixer until soft peaks form. You want the cream to hold its shape but still be soft and billowy. Peel the bananas and slice them into ½ cm rounds. Toss them gently in a small bowl with the lemon juice to coat.

Assemble the pudding. Take a 2-litre baking dish or a large glass bowl. Spread a thin layer of the cold custard on the bottom. Arrange a layer of vanilla wafers on top, covering the custard. Next, add a layer of banana slices. Spoon a third of the remaining custard over the bananas and spread it gently. Repeat the layers: wafers, bananas, custard. Finish with one final layer of wafers and bananas. Top with all the whipped cream, spreading it to the edges to seal in the pudding. The cream acts as a lid.

Chill and set. Cover the dish with cling film and refrigerate for at least 4 hours, but ideally overnight. As it rests, the wafers will soften and absorb the custard, creating a beautiful, tender, cake-like texture. The flavours will deepen and meld together. When you pull it from the fridge, the surface should be cool and firm to the touch.