Preheat the oven to 350°F. Line a muffin tin with liners. If you don’t have liners, grease the muffin tin generously with melted unsalted butter.
In a large bowl, mash the bananas until broken down but still slightly chunky — some banana pieces are fine.
Add the half-and-half, eggs, brown sugar, vanilla, cinnamon, and nutmeg to the bowl and whisk until combined.
Add the brioche cubes and gently toss until evenly coated in the custard.
Fold in the chocolate chips and chopped walnuts.
Divide the mixture evenly between the muffin liners, pressing down gently so the bread is compact.
Bake for 20 to 25 minutes, until puffed and golden brown on top.
Let cool slightly before removing from the pan, and enjoy warm with maple syrup and/or powdered sugar.