Preheat the oven to 180°C, fan 160°C, gas 4. Line a 12-hole cupcake tin with paper cases.
Cream the butter and sugar together until light and fluffy, then add the vanilla extract, eggs and 1 tablespoon flour. Whisk until combined, then add the remaining flour and whisk again.
Pour half the mixture into the cases. Add 1 teaspoon jam to each case and top with the remaining mixture. Bake for 20 minutes, until risen. Leave in the tin for 2 minutes, then cool on a wire rack. Dust with icing sugar before serving.
Cook’s tip: you can use any kind of jam for the ‘surprise’ – just whatever you have in the cupboard. Or for something really special, use a square of chocolate.