Preheat oven to 300°
Beat eggs in the bowl of a mixer, then slowly add the melted butter while mixer is still going.
Add all of the wet ingredients and mix until semi-smooth.
Add the remaining dry ingredients slowly until well incorporated.
If adding fruit or nuts, mix in at the very end by hand.
Pour mixture into prepared muffin tins (either greased or lined) and bake for 30-35 minutes