Prepare a rimmed baking sheet by lining it with a piece of aluminum foil, then butter the aluminum foil all over. Alternatively, line the baking sheet with a silicone baking mat. Set aside.
In a 2 quart microwave safe mixing bowl, place the sugar, light corn syrup, salt and peanuts. Stir to combine, then microwave on high for 4 minutes.
1 cup granulated sugar, ½ cup light corn syrup, ½ teaspoon salt, 1 cup raw peanuts
Very carefully remove the mixing bowl and give a quick stir before microwaving for another 4 minutes. Carefully remove the hot bowl and place it on a heat safe counter.
Add the unsalted butter and vanilla extract. Stir quickly to combine, then add the baking soda. Stir to combine all the ingredients, then quickly and carefully pour the mixture onto the prepared rimmed baking tray.
Using a rubber spatula, spread the peanut brittle into an even layer in a rough 8x10 size rectangle.
Allow the peanut brittle to cool on the counter for a minimum of 30 minutes, up to an hour, before breaking it into smaller pieces.
Notes
Tips:
Use a 2 quart (8 cup) microwave safe glass measuring bowl with a handle. The sugar and the bowl get extremely hot and the handle is what makes it possible to move and stir safely.
Do not put the hot bowl in a cold sink or under water. Let it cool completely on the counter first or you risk the glass shattering.
Use light or clear Karo syrup. Medium or dark corn syrup will make the brittle very dark with a much stronger flavor than traditional peanut brittle.
Storage:
Store the peanut brittle at room temperature in a sealed container for up to 1 month.