Use very ripe bananas with lots of brown spots for best banana flavor and sweetness., Avoid overmixing batter after adding flour to keep blondies chewy, not tough., Remove blondies from oven when a toothpick comes out with a few moist crumbs; they will continue to set as they cool., Use a light pan when browning butter to monitor color changes and prevent burning., Fold in toffee bits last if they soften or melt, reserving some to sprinkle on top before baking., Line pan with parchment paper with overhang for easy lifting and neat slicing., For nut-free version, omit nuts and increase chips or add sunflower seeds., For extra banana flavor, add 1/2 teaspoon ground cinnamon and 1 teaspoon banana extract., Peanut butter swirl variation: dollop softened peanut butter and swirl before baking., For mini muffins, bake in lined mini muffin tin for 12–15 minutes., For gluten-free, substitute all-purpose flour with a gluten-free blend that contains xanthan gum., To store: keep at room temperature up to 2 days, refrigerate up to 5 days, or freeze up to 3 months in individual squares.