Heat oven to 350*F. Line the bottom of an 8-inch square pan with buttered parchment.

Add the butter to a small saucepan set over medium heat. Melt the butter, then cook an additional minute or two, stirring constantly, until it becomes golden brown and smells caramely and slightly nutty. Remove from heat and stir in the brown sugar. The sugar will melt and combine with the butter to form a thick, soft mass that feels a little like a tootsie roll. Let cool.

Stir the egg, egg yolk, and vanilla into the cooled sugar. At the point, the batter will be thin and smooth. Add the flours, stirring until just blended. Fold in the mashed banana and toffee chips.

Pour the batter into the prepared pan. Bake 25-35 minutes, or until the center is slightly springy and a toothpick inserted into the center comes out clean. Let blondies cool completely before slicing and removing from the pan.