1) Preheat oven to 180 degrees C/ gas mark 4. Line 24 muffin tins with paper liners.
2) Using a hand mixer or standing mixer, cream the butter and vanilla sugar together until fluffy, about two to three minutes. Add eggs, one at a time and vanilla essence, beating until smooth.
3) Combine the flour, nutmeg, bicarbonate of soda and salt in a medium bowl. Add half the flour mixture to the creamed butter, mix to combine, then add the sour cream, mix to combine, and then the rest of the flour. Beat until well combined, taking care not to over mix. Gently fold in the chopped apples.
4) Divide batter between prepared muffin tins, filling them half way full. Bake until a toothpick inserted into the centre of the cupcakes comes out clean and the tops spring back when pressed gently, about 20 minutes. Cool the cupcakes in the tin on a rack for ten minutes then remove from the tin and cool completely.
5) Put apple puree into a small pastry bag with an open tip. Squeeze a small amount into the centre of each cupcake. Continue cooling completely. Then top with icing.
6) For the icing: Using a hand or standing mixer, beat cream cheese and butter together, at medium speed, until fluffy, about two minutes. Add in vanilla and lemon juice. On low speed, gradually add in icing sugar and beat until well combined. Ice as desired.
*Cook's Note: To make vanilla sugar, tuck a whole vanilla pod into some caster sugar. In day or two you have lovely vanilla flavoured sugar.