Preheat oven to 200 degree/400 F, 10 minutes before baking. Grease 12 hole (1/3 cup/80 ml) muffin pan. Combine flour, sugar and chocolate in large bowl. Stir in combined egg, buttermilk, butter and essence. Spoon mixture into prepared pan, top with berries, press down gently. Bake in the preheated oven for about 20 minutes. Serve dusted with sifted icing sugar, if desired.
Notes
As you can see in the picture I used only blueberries and adjusted the total quantity of berries accordingly. No need to defrost the frozen berries. I used Lindt classic white chocolate for this recipe. I used buttermilk & egg at room temperature. I stored it at room temperature for 3 days.