Preheat your oven to 350 degrees. Now, let's brown that butter! In a small saucepan, heat the butter over medium heat, stirring occasionally until the butter begins to foam and you start to see little brown specks. Cook for another minute then take butter off the heat and allow to cool for 1-2 minutes.

In a large mixing bowl with whisk, combine the slightly cooled brown butter and granulated sugar (it will look like wet sand). Next, add the vanilla and eggs and mix until well combined and smooth.

In a separate bowl, mix the flour, baking powder, salt, and espresso powder together. Then add that flour mixture to the butter mixture and using a spatula fold it in gently until combined.

Prepare your 8x8 brownie pan with parchment paper hanging over the edge for easy removal. Then pour your batter into the pan.

Next, mix your hot espresso, brown sugar, and flour together until combined and smooth. Pour this over your blondie batter and using a knife or chopstick (that's what I use) gently swirl it into the blondie batter then level the top.

Bake for 23-26 minutes or until the edges are set but the blondies themselves may seem underdone and undercooked. This is fine! Do not overbake these or they will end up dry and cakey instead of that heavenly chewy, gooey blondie that you want!

Set the pan on a cooling rack, and cool completely in the pan before removing and cutting into squares.