Begin by melting 1 cup of unsalted butter in a medium saucepan over medium heat. Stir continuously for about 5-7 minutes until the butter turns golden brown and emits a nutty aroma. Remove from heat and let cool for about 30 minutes.

In a stand mixer, beat the cooled brown butter with ¾ cup of brown sugar and ½ cup of granulated sugar together on medium speed until light and fluffy (3-4 minutes).

Add in 1 large egg and 1 teaspoon of vanilla extract to the mixing bowl. Mix on low speed until just combined.

In a separate bowl, whisk together 2 cups of all-purpose flour, ½ teaspoon of baking powder, ½ teaspoon of baking soda, and ½ teaspoon of salt. Gradually add the dry mixture to the wet ingredients and mix gently until just combined.

Carefully fold in 1 cup of toffee bits to the dough until evenly distributed.

Scoop the dough into balls (about 1.5 tablespoons each) and place them on a parchment-lined baking sheet. Cover tightly and refrigerate for at least 2 hours, preferably up to 24 hours.

Preheat your oven to 350°F (175°C). Line another baking sheet with parchment paper.

Place the chilled dough balls on the prepared baking sheet, spacing them about 2 inches apart. Lightly sprinkle with flaked sea salt. Bake for 11-13 minutes, until the edges are golden brown.

Allow the cookies to cool on the baking sheet for about 5-7 minutes before transferring to a wire rack to cool completely.