Salted Butterscotch Chocolate Chunk Cookies

In a medium saucepan, melt the butter over medium heat. Once it begins to bubble vigorously, cook for another 6 to 8 minutes, swirling occasionally, until the bubbles subside and turn into foam, and toasty brown flecks begin to float on the surface. Take off the heat and scrape the bottom of the pan. Pour the browned butter into a heatproof liquid measuring cup. Add a couple ice cubes (or a couple tablespoons of cold water) until you have 1 ¼ cups liquid. Add the vanilla extract, stir and set brown butter mixture aside to cool slightly.

In a medium bowl, whisk together the flour, baking powder and baking soda.

In a large bowl, whisk together both sugars and the brown butter mixture until well combined. Add the eggs one at a time, whisking thoroughly after each addition, until the mixture is very smooth, about 1 minute. Add the flour mixture to the brown butter mixture and mix to fully incorporate. Fold in both types of chopped chocolate and the toffee bits.

Using a ¼-cup cookie scoop or measuring cup, scoop mounds of dough (about 100 grams each) onto a baking sheet. Tightly wrap the baking sheet and refrigerate for at least 6 hours and up to 48 hours.

When ready to bake, heat the oven to 350 degrees with racks in the top and bottom thirds of the oven. Line 2 large rimmed baking sheets with parchment paper. Place 6 cookies onto each prepared sheet and bake for 18 to 20 minutes, moving the sheets between the racks and rotating them halfway through, until the cookies have spread slightly and their edges are golden.

Immediately sprinkle the tops of the cookies with flaky sea salt and let cool on the baking sheets for at least 10 minutes before transferring them to a wire rack to cool completely. Repeat with the remaining dough on a single baking sheet. (You can also freeze the balls of dough and bake them for about 20 to 22 minutes.) Cookies will keep, covered at room temperature, for up to 3 days.