Mix the flour and baking powder. Melt the butter and let cool slightly, so that it is still liquid. Mix the egg, honey, yogurt and sour cream and stir in the melted butter. Then work in the flour and fold in the blueberries. All the ingredients should be well combined. Put the paper baking cups in the holes in the muffin pan and fill 3/4 full with the muffin batter. Bake in a preheated oven (180°C/350°F with top and bottom heat) for 25-30 minutes, until golden brown. Take out of the oven, let rest in the pan for 5 minutes, then take out and let cool. Serve dusted with confectioners' sugar.