You’ll need:

For the cupcakes:
125g (1 stick plus about 1 tbsp) unsalted butter, at room temperature
155g (3/4 cup) sugar
2 eggs
225g (about 1 + 3/4 cups) self-raising flour + 1/4 tsp salt

1/3 cup milk
1/4 tsp vanilla extract

Optional: 1/2-2/3 cup mini semi-sweet chocolate chips (or finely chopped chocolate)

55 g (4 tbsp) unsalted butter, at room temperature
6 tbsp light brown sugar, packed
1 cup plus 2 tbsp (about 135g) all-purpose flour
1/2 can (200g/7 oz) sweetened condensed milk
1/4 tsp vanilla extract

1/4 cup mini semisweet chocolate chips (or finely chopped chocolate)

350g (3 sticks) unsalted butter, chopped into cubes

400g (about 3 1/4 cups) icing/confectioner’s sugar, sifted

1/2 can (200g/7 oz) sweetened condensed milk

To decorate: milk bottle candies, mini chocolate chip cookies