Make the crust. Place the digestive biscuits in a sealed bag and bash them with a rolling pin until they resemble fine, sandy crumbs. You should hear a satisfying crunch as they break down. Tip them into a bowl and stir through the melted butter and sugar until the mixture feels damp and clumps together when you press it.

Blind bake the base. Press the crumb mixture firmly and evenly into the base and up the sides of a 23cm loose-bottomed tart tin. Use the flat bottom of a glass to get a smooth, compact finish. Bake at 160°C (140°C fan) for 10 minutes. The kitchen will smell warmly of toasted biscuit. Remove and let it cool completely on a wire rack.

Whip the filling. In a large, clean bowl, whisk the egg yolks with an electric mixer until they are thick and pale, the colour of a primrose, and they leave a ribbon trail on the surface when you lift the beaters.

Add the condensed milk. Pour in the condensed milk and whisk on low until fully combined. The mixture will become thick and velvety, like a very rich custard.

Introduce the lime. Slowly stream in the key lime juice while whisking gently. Watch as the mixture thickens almost immediately, turning a pale, creamy yellow. This is the magic of the acid reacting with the milk. Fold in the lime zest until it is evenly distributed, and the air smells sharp and fragrant.

Bake the filling. Pour the filling into the cooled biscuit base and spread it level. Bake at 160°C (140°C fan) for just 12 minutes. The edges should look set, but the centre will still wobble slightly when you gently shake the tin. Do not let it brown. The smell will be a gorgeous, sweet-tart perfume.

Cool and chill. Let the pie cool completely on the rack at room temperature. You will see the surface settle and become smooth. Then, transfer it to the fridge to chill for at least 4 hours, or ideally overnight. The filling will firm up to a silky, sliceable texture.

Top and serve. Just before serving, whip the double cream, icing sugar, and vanilla extract together until soft peaks form. The cream should be billowy and hold its shape. Spread or pipe it over the chilled pie, then garnish with a little extra lime zest. My kids absolutely devour this every time I make it.