Lightly butter a baking sheet and place on a cutting board, folded towel or cooling rack. Have two forks or a spoon ready to spread the hot mixture.
Stir together sugar and light corn syrup in a large microwave-safe glass bowl. It will look like a sugar scrub paste. I use a Pyrex bowl I’ve had for 20+ years. Cover tightly with plastic wrap. This step replaces step in traditional method of washing down the sugar crystals. Covering with plastic wrap can be optional but I've found it to be helpful to reduce crystalization and produce smooth textured brittle.
Microwave (1100 watts) the sugar mixture in the bowl on HIGH for 3 minutes to wash down any crystals from sides of the bowl.
While the sugar and corn syrup mixture is cooking in the microwave, take this time to measure your peanuts, butter, vanilla and baking soda.
Removethe bowl from microwave with pot holders or oven mitts. It's hot! Place the bowl on a folded towel or cutting board or stovetop grate. Then, uncover bowl, removing plastic wrap away from you to avoid steam.
Most critical step: Microwave, uncovered, 4 minutes or until the mixture begins to turn golden on the bottom. If it's amber color at this point, it's gone too long.
This can happen fast! Once it starts to turn golden, it will continue turning darker, even as you are removing it from the microwave. Remember, it's HOT!
Carefully remove the bowl with pot holders and stir in the cocktail peanuts and butter until the butter melts. It will be sticky.
Microwave another 1 minute or until the mixture is almost all bubbly on top.WATCH CAREFULLY through the microwave window. Have baking soda and vanilla already measured out.
Carefully, remove the bowl from microwave with potholders. Quickly stir in baking soda and vanilla. It will bubble up.Immediately pour hot candy mixture onto the buttered baking sheet, then spreading it out with two forks or a spoon. Let cool completely and break into pieces. Store in an airtight container. Yield: 15 ounces peanut brittle