To make the cupcakes, preheat the oven to 180C, gas 4. Line the cupcake tin with 12 cupcake cases. In the bowl of a stand mixer, combine the flour, sugar, butter and baking powder using the paddle attachment. Mix on a low speed until the mixture resembles fine breadcrumbs. You shouldn't see any large lumps of butter. Alternatively, use your fingers to rub the butter into the flour and sugar.
In a small jug, use a fork to blend the eggs, milk, lemon zest and vanilla bean paste together. Add the mixture a little at a time to the bowl, beating until it is all combined. Keep beating for a few minutes more, until the mixture is uniform and smooth with no lumps.
Divide the mixture between the cases evenly, filling each one no more than two-thirds full. Bake in the preheated oven for 16-18 minutes, until a skewer inserted comes out clean and the cakes are a pale golden brown. Don't be tempted to over-bake here; get them out as soon as the skewer is clean. The last thing you want is dry cakes!
Leave to cool for five minutes in the tin, then remove and leave to cool completely on a cooling rack. Do not attempt to decorate them until they are cold.
To make the icing, put the cream cheese into a large bowl, and use an electric hand-held whisk to beat it until smooth. Add the icing sugar, a few tablespoons at a time, until it is all incorporated. Mix in the double cream and whisk until the mixture thickens. You can whisk this by hand, but it will take a few more minutes to thicken. It won’t hold its shape yet, so it is important to chill it in the fridge for at least an hour so that it firms up.
Put the biscuits for the topping in a sealable plastic bag, seal it and then, using a rolling pin, lightly bash the bag to crush the biscuits into small pieces.
Add the biscuit crumbs to the melted butter and stir until the mixture starts to clump together.
To assemble, use a sharp knife or specialist cupcake corer to make a circular incision in the centre of each cupcake. Take out the middle and fill each cavity with ½ teaspoon of lemon curd.
When the icing has set, put it into a disposable piping bag. Cut the end off the bag, making a medium-sized circular hole, then pipe a double ring around the edge of the lemon curd, and fill the gap with the remaining lemon curd.
Sprinkle the biscuit topping around the icing ring, trying to avoid the lemon curd centre. These cupcakes need to be stored in the fridge, where they will keep for up to three days.