Mix flour, sugar, baking powder and salt in a bowl. Combine the eggs, oil and butter. Add the milk and butter; stir into the dry ingredients until just moistened. Stir in berries, nuts and mandarins. Spoon into greased muffin pans to 2/3 full. Bake in a 400F oven for 18 minutes or until light golden brown on top. Makes 12 muffins.