Oil a 20 x 20cm square cake or brownie tin and line with baking parchment. Heat the oven to 180C/160C fan/gas 4. Tip the egg whites into a large bowl and beat to stiff peaks using an electric whisk. Beat in half the sugar, 1 tbsp at a time, until stiff and glossy. Set aside.

Tip the rest of the sugar, the vanilla and egg yolks into a second large bowl, and whisk for 3-4 mins until voluminous and foamy. Add the oil and whisk to combine. Sift in the flour, baking powder and a pinch of salt. Fold to combine, then fold in the whipped egg whites, being careful not to knock out all the air.

When everything is combined, pour the mixture into the prepared tin and tap firmly on a work surface to break up any large air bubbles (this will ensure it bakes evenly). Bake for 25-30 mins, or until a skewer inserted into the middle comes out clean. Firmly tap the tin on a work surface again, then leave to cool completely.

Meanwhile, tip the three types of milk into a bowl, add the lime zest and whisk together to combine.

Invert the cake onto a large tray with high sides. Poke small holes all over the cake using a skewer. Pour most of the milk mixture over the cake and leave to absorb for 5 mins. Pour the remaining mixture over and transfer to the fridge for 2 hrs.

For the topping, pour the cream, condensed milk, most of the lime zest and juice into a large bowl. Whip to soft peaks using an electric whisk, then spoon over the cake. Scatter over the remaining lime zest before serving. Will keep chilled for up to two days.