Brown the butter in a medium saucepan over medium heat for about 5-7 minutes, stirring constantly until golden brown.

Once browned, stir in espresso powder and transfer to a bowl to cool until solidified, which may take 1-2 hours.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a stand mixer, combine cooled butter with brown sugar and granulated sugar; beat on medium-high speed for 3-4 minutes until light and fluffy.

Add egg and vanilla extract to the sugar and butter mixture, mixing on medium speed for about 1-2 minutes until well incorporated.

In a separate bowl, whisk together flour, baking powder, baking soda, and salt.

Gradually add dry mixture to wet mix in the stand mixer on low speed, mixing just until combined.

Fold in Heath toffee bits using a spatula.

Scoop dough into large balls and place on the prepared baking sheet; refrigerate for at least 24 hours.

Preheat oven to 350°F (175°C) and arrange dough balls on the baking sheet, spacing them apart.

Sprinkle tops lightly with sea salt and bake for 11-13 minutes until edges are golden brown.

Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack.