In a medium saucepan over medium heat, melt the butter, swirling occasionally until it turns golden brown, about 5-7 minutes.

Transfer the browned butter and espresso mixture to a mixing bowl, then let it cool until it's slightly solidified, about 30 minutes.

Use an electric mixer to cream the cooled browned butter with both sugars in a large bowl until light and fluffy, about 2-3 minutes.

Add one large egg and vanilla extract into the creamed butter mixture, mixing until well combined.

In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add to wet mixture, mixing until just combined.

Fold in the Heath toffee bits gently with a spatula until evenly distributed.

Using a large cookie scoop, portion out dough balls onto a tray lined with parchment paper and refrigerate for at least 2 hours.

Preheat your oven to 350°F (175°C) about 20 minutes before baking.

Space the chilled dough balls on prepared baking sheets and sprinkle a pinch of flaked sea salt on top of each cookie.

Bake for 11-13 minutes, until the edges are lightly golden and the centers are still soft.

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