Preheat your oven to 175 degrees (fan) and line a muffin tray with cases or parchment paper
In a large bowl, use an electric hand mixer or stand mixer to beat the butter and sugar until light and fluffy
Mix in the eggs and extra yolk one at a time until fully combined
Stir in your mash bananas until smooth and combined
Fold in the flour gently using a rubber spatula but don’t over mix or you’ll end up with dry bread
Fold through your chopped chocolate chunks
Divide the banana bread batter evenly into your 12 muffin cases and bake on the middle rack for 20-25 minutes until golden brown