In a medium saucepan, melt the butter over medium heat, stirring occasionally until golden brown (5-7 minutes). Stir in the espresso powder, chill until solidified (1-2 hours).

Beat the solidified butter with granulated sugar and brown sugar on medium speed until light and fluffy (3-4 minutes).

Add the egg and vanilla extract, mixing on low speed until combined and smooth (about 1 minute).

In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add to the cookie dough on low speed until just incorporated.

Gently fold in the toffee bits using a spatula.

Portion the dough onto a lined baking sheet; refrigerate for at least a few hours or overnight.

Preheat the oven to 350°F (175°C). Prepare a baking sheet with parchment paper.

Bake the dough balls spaced 2 inches apart for 11-13 minutes until edges are golden and centers look slightly soft.

Allow the cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.