Line a 12 tin muffin tray with muffin cases.
Cream the butter and sugar together in a large mixing bowl until pale and fluffy. Slowly add the beaten eggs, whisking constantly at the same time until incorporated. Sift in the flour and baking powder, mix well, then fold the blueberries in carefully. Cover and chill for at least an hour.
Preheat the oven to 190°C when ready to bake, then spoon the batter evenly into the muffin cases. Bake for 18-22 minutes until golden and risen.
Remove when ready and allow to cool a little before turning out onto a wire rack. Remove the paper cases, serve warm or cold.