Prepare your workspace by lining a 9x13-inch baking dish with parchment paper.

Remove stems and seeds from jalapeños, finely dice them and set aside.

Combine granulated white sugar, light corn syrup, and a splash of water in a medium saucepan over medium heat.

Monitor the mixture, stirring gently until it boils and becomes clear, about 5-7 minutes.

Attach a candy thermometer and cook until the temperature reaches 250°F (121°C).

Stir in salted peanuts and jalapeños, continuing to heat until reaching 300°F (149°C).

Remove from heat and stir in unsalted butter, baking soda, and vanilla extract.

Pour the mixture into the prepared baking dish and spread evenly.

Allow the brittle to cool at room temperature for about one hour before breaking it into pieces.