Set out a medium heat-proof bowl because you’ll need it at the end of this step. Slice the butter into Tablespoon-size pieces and place in a light-colored skillet or large pot. Light colored helps you determine when the butter begins browning. (See note if using a dark skillet or pot.) Melt the butter over medium heat and stir or whisk constantly. Once melted, the butter will begin to foam. Keep stirring/whisking. After 5-7 minutes, the butter will begin browning and you’ll notice lightly browned specks begin to form at the bottom of the pan. It will have a nutty aroma. Once browned, remove from heat immediately and pour into the bowl, including any solids that have formed on the bottom of the pan. (You want those solids for flavor.) Cool brown butter for 5 minutes. Don’t cool longer than that because the butter will begin to thicken and, as a result, the cookie dough will be difficult to mix and its texture will be too crumbly.

Whisk the brown sugar and granulated sugar into the brown butter and then whisk in the eggs and vanilla extract. Set aside. In a large bowl, whisk the flour, baking soda, and salt together. Pour the wet ingredients into the dry ingredients, add the chocolate chips and toffee, then stir together with a large spoon or silicone spatula. The dough will seem too dry at first, but keeping stirring until it comes together. Dough will be greasy, thick, and a bit crumbly.

Scoop dough into balls, about 1 and 1/2 Tablespoons of dough each, and place on a large plate or baking sheet. I like to roll each cookie dough ball between my hands to smooth them out since they can be a little crumbly. Cover and chill the cookie dough balls in the refrigerator for 2 hours and up to 3 days before baking. (You can also freeze the dough balls, see Freezing Instructions below.)

Towards the end of chill time, preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.

Arrange cookie dough balls 3 inches apart on prepared baking sheets. If desired, lightly sprinkle coarse sea salt on top of each. Press the salt down into the cookie dough balls if it’s not sticking.

Bake for 12-13 minutes or until the edges are lightly browned. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. While the cookies are still warm, I like to press a few more chocolate chips or toffee pieces into the tops—this is only for looks! Cookies are extra soft out of the oven, but become chewier as they cool.

Cookies stay fresh covered at room temperature for up to 5 days or in the refrigerator for 1 week.