Butter a large rimmed cookie sheet or jelly roll pan or simply spray it with cooking spray.
In a small bowl, combine cinnamon, nutmeg, and baking soda. Set aside.
In a large glass bowl that is suitable for the microwave, combine sugar and light corn syrup.
Place bowl in microwave oven. Microwave on high for approx. 4 minutes.
Carefully remove the bowl from the microwave. It will be hot.
Stir mixture with a silicone spatula and return to the microwave for an additional 3 to 5 minutes. Keep an eye on the sugar and corn syrup mixture and remove when it becomes light golden brown in color. If it gets too dark, it may be burnt.
Remove from the microwave with pot holders, as the bowl and ingredients will be very hot. Stir in the vanilla and butter, until combined.
Stir in the cinnamon, nutmeg, and baking soda mixture. Stir in the salted, roasted peanuts.
If you like things extra salty, add a pinch of salt.
Using a silicone spatula or spoon sprayed with no-stick spray, spread the mixture onto your greased baking sheet. Spread it out evenly until it is about the same thickness as the peanuts.
Allow peanut brittle to sit for about 1-2 hours or until hardened. Mine is usually ready within a hour, but it may vary depending on where you live and the humidity level. Using your hands, break peanut brittle into pieces.