01 - In a medium saucepan over medium heat, melt the butter. Continue cooking, swirling often, until it foams, turns golden, and smells nutty (about 4-5 minutes). Immediately transfer to a large mixing bowl to cool for 10 minutes.
02 - Preheat the oven to 350°F. Line two baking sheets with parchment paper.
03 - Add mashed banana, brown sugar, and granulated sugar to the cooled brown butter. Whisk until well combined and smooth.
04 - Beat in eggs, one at a time, then vanilla extract.
05 - In a separate bowl, whisk together flour, baking soda, baking powder, and salt.
06 - Gradually add the dry ingredients to the wet mixture, mixing just until combined.
07 - Fold in chocolate chips and toffee bits.
08 - Scoop dough (about 2 tablespoons per cookie) onto prepared baking sheets, spacing 2 inches apart. Optionally, sprinkle with flaky sea salt.
09 - Bake for 11-13 minutes, until edges are golden and centers are just set. Do not overbake.
10 - Cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.