In a large bowl, whisk together the dry ingredients.
In a separate bowl, whisk together the egg, oil and milk.
Using a rubber spatula, fold the wet mixture into the dry mixture until just combined.
Take the muffin tin out of the oven. Brush the melted butter generously on the bottom and sides of each mini muffin cavity. Spoon some of the batter evenly into the mini muffin mold.
Place the muffin tin in the oven and bake for 20-23 minutes, or until a toothpick stuck in the middle of a mini muffin comes out clean. Remove from the oven and let cool slightly before trying to remove mini muffins.