Spray a large rimmed baking sheet with cooking spray, line with a piece of parchment paper, and spray the paper. Spray a metal spatula as well.
In a large microwave-safe bowl, stir together the sugar, corn syrup, and salt until smooth. Microwave the sugar mixture on high until it is bubbling, 2 to 4 minutes. Mix in the peanuts and butter and microwave on high until the mixture has thickened and is a pale golden color, 3 to 5 minutes more.
Remove the peanut mixture from the microwave and stir in the vanilla and baking soda. (Be careful, as the mixture will bubble up.) Immediately pour the mixture into the prepared pan, spreading it with the prepared spatula. Let stand until hardened, 20 to 30 minutes. Lift the brittle off the parchment and break into 2-inch pieces.
Storage suggestion: Keep the peanut brittle at room temperature, between sheets of wax paper in an airtight container, for up to 5 days.