Moist double-chocolate banana muffins loaded with chocolate chips and topped with more chips and crunchy walnuts. This recipe makes 12 jumbo bakery-style muffins (or about 24 regular muffins).
Preheat the oven to 375°F. Spray two 6-cup jumbo muffin pans with nonstick cooking spray, or line them with jumbo muffin liners.
In the bowl of a stand mixer (or a large bowl with a hand mixer), mash the bananas on low to medium speed until mostly smooth.
Add the eggs, vanilla, oil, milk, and sugar, mixing on low speed after each addition until well combined.
Add the cocoa powder, salt, and baking soda and mix on low until blended. Add the flour and mix on low just until no dry streaks remain; don't overmix.
Stir in half of the chocolate chips (⅓ cup).
Divide the batter evenly among the 12 jumbo muffin cups. Sprinkle the remaining chocolate chips and the chopped walnuts over the tops, pressing them in lightly.
Bake for 20 to 25 minutes, or until a toothpick inserted in the center of a muffin comes out clean or with a few moist crumbs (not melted chocolate).
Cool in the pans for 10 minutes, then run a knife around the edges and transfer the muffins to a wire rack to cool.
Notes
For regular-size muffins, fill a greased standard muffin pan about three-quarters full and bake 16 to 20 minutes; the recipe makes about 24.Store cooled muffins airtight at room temperature for up to 2 days, in the fridge for up to 5 days, or wrapped in the freezer for up to 3 months.