Place all of the ingredients, in the order listed, into a large blender.
Blend on high until smooth. Let sit for 5 minutes.
Stir in any additional mix-ins such as chocolate chips or blueberries, or leave the muffins as is.
Pour the batter evenly into a 12-cup greased muffin tin.
Bake in a preheated 350-degree oven for 20 minutes.
Let cool for 5 minutes before removing from muffin tin.
Store in the fridge for up to a week.