2) In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar until light and fluffy, about 5 minutes. With the mixer on a low speed, add the eggs 1 at a time, then add the vanilla, sour cream and milk.
3) In a separate bowl, sift together the flour, baking powder, bicarbonate of soda and salt. With the mixer on a low speed add the flour mixture to the batter and beat until just mixed. Fold in the blueberries with a spatula and be sure the batter is completely mixed.
4) Scoop the batter into the prepared muffin pans, filling each paper case just over the top. Bake for 25 to 30 mins, until the muffins are lightly golden on top and a cocktail stick comes out clean when inserted into the centre of the cake.