Preheat oven to 175 degrees C. Lightly grease 12 cup muffin cups
Mix the flour, baking powder, baking soda, and salt together in a mixing bowl
Stir the melted butter, egg, milk, in a large mixing bowl until evenly blended
Slowly stir in the flour mixture to form a batter
Add the fillings and mix
Spoon about 2 tablespoons into each muffin cup
Bake in preheated oven for about 35 minutes, until a toothpick inserted into the centre of a muffin comes out clean
The quantities listed above makes 12 muffins. I usually double up and bake 24 at a time. The majority go into the freezer for when required.