In a glass 2 cup measuring cup combine and stir together the sugar and corn syrup.
Microwave on full power for 3 minutes. The time is for a 700-watt microwave, yours may take a shorter time depending on the wattage of your microwave.
Carefully remove the measuring cup from the microwave and stir in the peanuts. Return to microwave and heat on 100% power for another 3 minutes
Next, remove the measuring cup from the microwave and stir in the butter and vanilla. return the mixture to the microwave and heat for 1 more minute.
Next, stir in the baking soda to the measuring cup and microwave for another for about 15 to 20 seconds
Let the mixture sit until it stops bubbly and settles down.
Pour the mixture onto a parchment-lined small rimmed baking sheet. Smooth out with a scraper or the back of a spoon coated with a non-stick spray. Allow the candy to cool completely.
When candy is cooled completely, lift out by the edges of the parchment paper and cut with a sharp knife or use a hammer to break apart.
Notes
Use a Microwave-Safe Bowl: Choose a large, microwave-safe bowl for this task. The sugar mixture will bubble up in the microwave, so ensure the bowl is big enough to prevent it from boiling over.Stir Carefully: It's crucial to stir the mixture carefully between microwave sessions to avoid hot spots and ensure even cooking.Watch Your Timing: Every microwave is different, so your cooking times might vary. Start by microwaving for shorter intervals and keep a close eye on the mixture's color and consistency. You're aiming for a light amber color and a smooth texture.Use a Candy Thermometer: If you have one, use a candy thermometer to take the guesswork out of figuring out if your brittle is done. The temperature should reach 300°F (150°C), also known as the hard-crack stage in candy making.Add Baking Soda at the End: Adding baking soda to the hot sugar mixture will cause it to foam up, which gives brittle its distinctive texture. Make sure you stir it in quickly and thoroughly, then immediately pour the mixture onto your prepared baking sheet.Prepare Your Baking Sheet: Before you start cooking, prepare your baking sheet by greasing it or lining it with a silicone mat or parchment paper. This will make it easier to remove the brittle once it has set.Spread the Mixture Thinly: When pouring the hot mixture onto the baking sheet, spread it as thinly as possible. The thinner the brittle, the easier it will be to eat.Let It Cool Completely: Allow the brittle to cool completely before breaking it into pieces. Trying to cut or break it while it's still warm may cause it to stretch and become chewy instead of crisp.