Combine the first 4 ingredients in a small saucepan over medium heat. Cook 8 minutes, or until golden-brown. (Keep an eye on it—this can go from just right to burned in no time. Hint: as the bubbling slows down, you’re getting close.)
While the sugar mixture cooks, place a silicone baking mat on a work surface. Have a large piece of parchment paper and a rolling pin handy.
When sugar mixture is done, working quickly, remove the pan from the heat, and whisk in the salt and baking soda. Stir in nuts. Pour mixture onto baking mat. Cover with parchment paper, and roll it as thin as possible (about 1/8 inch). Don’t worry if the parchment paper sticks to the warm brittle—you’ll be able to peel it away once the brittle cools.
Cool, break into pieces, and store in an airtight container.