Prep for baking banana blueberry muffins. Preheat the oven to 325 degrees F. Line a nonstick, dozen muffin tin with cupcake liners, or spray the pan with cooking spray or brush with a little melted butter.
Mix together wet ingredients. In a large bowl, mash bananas with the back of a fork. Add butter, almond extract, and whisked eggs. Mix together loosely.
Mix together dry ingredients. In a separate bowl, mix together dry ingredients: flour, sugar, baking powder, salt, and spices. Add dry ingredients to wet ingredients and combine with a fork until no dry ingredients are left.
Add frozen blueberries and raspberries to muffins. Gently fold blueberries and raspberries into banana muffin batter until incorporated.
Bake banana blueberry muffins for 30-40 minutes at 325 degrees F. When the muffin tops are completely golden brown and the inside comes out clean with a toothpick, they are done. Rest 5 minutes on a cooling rack before serving. The berries will be very hot right out of the oven.
Using frozen blueberries and raspberries increases the cook time (vs. fresh berries). Cooking muffins with frozen berries adds on 5-10 minutes of cook time.
If cooking these in a loaf pan, cook for ~60-70 minutes total.