Brown the Butter: In a medium saucepan over medium heat, melt the unsalted butter while stirring constantly. Cook until the butter turns golden brown and emits a nutty aroma, about 5-7 minutes. Be vigilant to prevent burning, as burnt butter can ruin the flavor.

Mix in Espresso Powder: Once the butter is browned, transfer it to a mixing bowl and immediately stir in the tablespoon of espresso powder. This will help the espresso dissolve better. Let the mixture cool in the refrigerator for about 1-2 hours until it firms up.

Prepare the Dough: Using a stand mixer, beat the chilled browned butter and both sugars (brown and granulated) on medium-high speed for 3-4 minutes. The mixture should become light and fluffy, indicating that air has been incorporated.

Add Egg and Vanilla: Mix in the room temperature egg and vanilla extract, beating until the mixture is smooth and well combined. Ensure the egg is at room temperature to help it incorporate better.

Incorporate Dry Ingredients: Gradually add the baking powder, baking soda, salt, and flour to the wet mixture. Mix on low speed until just combined to avoid overmixing, which can lead to tough cookies.

Fold in Toffee Bits: Gently fold in the Heath toffee bits with a spatula, ensuring they are evenly distributed throughout the dough.

Chill the Dough: Scoop the dough into large balls, about 2 tablespoons each, and place them on a plate. Refrigerate for at least 1 hour, or up to 24 hours for enhanced flavor and texture.

Preheat Oven & Bake: When ready to bake, preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Place the chilled dough balls on the sheet, leaving space between them, and sprinkle lightly with flaked sea salt. Bake for 11-13 minutes until the edges are golden brown and the centers look set.

Cool & Serve: Allow the cookies to cool slightly on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely. This helps them maintain their chewy texture.