Brown the butter in a medium saucepan over medium heat until it turns golden brown and has a nutty smell. Pour into a glass bowl and add espresso powder, mixing until no clumps remain. Refrigerate until solidified.

Place butter and sugars in a stand mixer bowl. Beat on medium-high speed until light and fluffy, about 3 to 4 minutes.

Add the egg and mix on low speed until smooth, about 30 seconds. Beat in vanilla.

Add baking powder, baking soda, salt, and flour mixture, mixing on low until just combined. Fold in toffee bits.

Scoop dough into large balls using a ? cup scoop. Chill for at least a few hours or overnight if possible.

Preheat oven to 350?F. Line baking sheets with parchment paper.

Place 8 cookie balls on the baking sheet and sprinkle with flaked sea salt. Optionally, add more toffee bits on top. Bake for 11-13 minutes until golden brown around the edges.

Allow cookies to cool on the pan before transferring to a cooling rack.