In a small saucepan, add the butter and brown sugar. Place over medium heat and stir frequently until it reaches 300 degrees F.

Immediately pour the hot toffee onto a parchment lined baking sheet. Allow to set until solid and cool.

Break the toffee into small pieces with your hands. Reserve a small amount for topping the cookie dough.

In a medium bowl, combine the flour, baking powder, and salt. Set aside.

Brown the butter: In a small saucepan, add 213g (15 tbsp) of unsalted butter and place over medium heat. As the butter melts, stir it with a rubber spatula to encourage even cooking. Once the butter has fully melted, it will alternate between rapid large bubbles and gentle small foamy bubbles. The butter will be ready once it turns a dark golden color and the fat solids have darkened and settled at the bottom of the pan. Immediately pour into a large bowl, scraping out the fat solids at the bottom, and weigh out to 170g (¾ cup).

To the brown butter, whisk in the sugars, then the egg and vanilla until fully combined.

Add the dry ingredients and fold until mostly combined.

Lastly, fold in the milk chocolate chunks and toffee pieces.

Using a 2 tablespoon cookie scoop, portion the dough onto a small parchment lined baking sheet. Chill in the fridge for at least 1 hour or overnight.

When ready to bake the cookies, preheat the oven to 350 degrees F and line two large baking sheets with parchment paper.

Place the chilled cookie dough balls on the baking sheet about 2 inches apart. Top each of them with more milk chocolate and toffee pieces, if desired. Bake the cookies for about 12 minutes until golden on the edges.

Once the cookies come out of the oven, immediately use a round cookie cutter or glass to scoot the edges in and make them perfectly round.

Allow them to cool for a few minutes on the baking sheet, then sprinkle with flaky sea salt and enjoy!