Place 16 mini silicone muffin cases on a baking sheet.
Melt the butter and leave to cool. Whisk the egg whites in a thoroughly clean bowl until frothy but not turning white and peaking.
Sift the flour and icing sugar into the bowl, then add the ground almonds. Stir the almond extract into the melted butter and add to the bowl. Using a large metal spoon, stir the ingredients gently together until combined. Divide among the cases so each is about three-quarters full and place several blueberries on top of each.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 12–15 minutes until risen and just firm to the touch. Leave in the cases for 5 minutes, then transfer to a wire rack to cool. Serve warm or cold dusted with icing sugar.