Heat oven to 350°F and set a rack in the middle. Line an 8 by 8-inch metal* baking pan with parchment paper or foil, leaving a little overhang.

Melt the butter in a medium, light-colored saucepan set on low heat. Once the butter is melted, turn the heat to medium and use a heat proof spatula to stir the butter and scrape the bottom of the pan as the butter foams and spatters. Once the butter quiets down, it will begin to smell nutty and will develop brown (not black) bits at the bottom of the pan, about 2-4 minutes. Pour butter into a small heat-proof bowl, making sure to scrape in the brown bits, and allow to cool while you whip the eggs.

Add the eggs to the bowl of a stand mixer fitted with the whisk attachment (or use a hand held mixer). Add in both sugars, salt and vanilla, and whip on high speed until the mix turns from runny and dark, to light, thickened and pale in color, from 7 to 10 minutes, depending on the power of your mixer.

Reduce speed to low and drizzle in the brown butter and bourbon. Once they are fully incorporated, add the flour all at once and continue mixing on low until roughly combined (if using a stand mixer, switch to the paddle attachment). Stir in the add-ins with a spatula until they are evenly distributed. Don’t over-mix.

Transfer the dough to the baking pan and smooth it with the back of a spoon or spatula. Bake for 25 to 30 minutes, until the edges are very light brown, but the center looks a little under-baked (it will firm up quite a bit as it cools). Let the blondies cool in the pan, then lift out onto a cutting board and and cut squares into your desired size.