Steps

1. Heat the oven to Gas Mark 4/180C
2. Whisk the egg, hard, until full of air. Add the sugar, gradually. Mix well, mix hard!
3. Add the softened butter, and beat hard again ? the mixture should be as light and air-filled as possible.
4. Add the buttermilk, and vanilla to taste.
5. Sift in the flour and bicarbonate of soda. Beat hard, until as smooth as you can get it.
6. Divide the mixture into four bowls. For pink pies, add a couple of drops of red food colouring to the mixture. For green pies, add a teaspoon of matcha powder. For yuzu-y yellow pies, add either a few good sprinkles of freeze-dried yuzu or, if you are lucky enough to find it, the rind and a good squeeze of the juice of yuzu. Leave as is for vanilla pies.
7. Line a tray with baking paper and use a piping bag to pipe out neat little blobs of mixture. For mini pies, think the size of a 50p coin. You will have to sandwich the blobs together once they are cooked, so try and be as consistent as possible. You can also use a spoon, but this is more hit-and-miss.
8. Bake for 12-13 minutes, remove and leave to cool. We baked ours in colour batches to avoid disaster.
9. Whilst your blobs are baking, make the filling. Mix the cream cheese, sifted icing sugar and butter together. Add a few drops of vanilla extract to taste, or customise ? we used 1tsp matcha powder in one batch, and 2-3tbsp ground sesame in the other. Mix well, and put in the fridge as you wait for your cake blobs to cool.
10. Once your cake blobs are cool, sandwich together at will.