Step 1

Position a rack in the center of the oven and preheat the oven to 350 ̊F. Have ready a rimmed 12×17-inch baking sheet.

Step 2

In a large heatproof bowl, combine the butter and sugar. Microwave on high power just until the butter is hot and almost completely melted and the sugar has begun to dissolve, about 2 minutes (alternatively, you can melt the butter and sugar together in a saucepan over medium heat, being careful not to bring the mixture to a boil).

Step 3

Remove the bowl from the microwave (or the saucepan from the heat) and whisk until the butter is completely melted. Let cool for 5 minutes. Whisk again continuously for 1 minute, or until the mixture is thickened and smooth and no longer appears separated. Whisk in the vanilla extract and salt. Stir in the flour until well incorporated. Stir in half of the nuts.

Step 4

Turn out the dough onto the sheet pan and pat it into a very thin, even layer with your hands (it won't look as if you'll be able to fill the entire pan, but you will--just keep on patting and spreading out the dough all the way to the edges of the pan. Use an offset spatula to give the dough a smooth finish. Sprinkle the chocolate chips and the remaining chopped nuts over the dough and press them lightly into it with your hands.

Step 5

Bake for 22 to 25 minutes, or until light golden brown and slightly firm to the touch all over, rotating the pan 180 degrees every 7 to 8 minutes to encourage even baking. Let cool in the pan for 3 minutes. Line a second sheet pan with parchment paper. Flip the brittle slab onto the paper and then immediately invert it right side up onto a cooling rack, peeling off the parchment. Cool completely. Break into pieces. Store in an airtight container for up to 5 days.