It's helpful to use a pot that's at least 3 quarts in size to accommodate the boiling mixture.
- 1 cup (200 g) white sugar
- 1/2 cup (150 g) light corn syrup
- 1/4 cup (57 g or 1/2 stick) unsalted butter
- 1/4 cup water
- 2 teaspoons vanilla extract
- 3/4 teaspoon baking soda
- 1/4 teaspoon kosher salt, omit if using salted peanuts
- 1 1/4 cups (175 g) unsalted dry roasted peanuts
1 Prep the baking sheet, baking soda, salt, vanilla, and peanuts: Spray a rimmed baking sheet with cooking oil and place on heatproof trivet or oven mitts.
Measure out the peanuts in a medium sized bowl, the baking soda and salt into a small bowl, and the vanilla in another small bowl.
2 Melt the sugar, corn syrup, and butter: Place the sugar, corn syrup, butter and water in a medium saucepan at least 3 quarts in size (in order to accommodate the boiling mixture after adding the baking soda).
Attach a candy thermometer to the side (if using). Turn the heat on high and gently stir with wooden spoon or heatproof spatula until the butter has melted and the sugar has dissolved.
If for some reason the sugar doesn't all dissolve and you see undissolved crystals stuck to the sides of the pan, just brush them down with a wet pastry brush. (This may not happen to you, so don't fret if you don't have a pastry brush. Just carry on; the brittle will be fabulous.)
3 Boil the caramel: Once the sugar has dissolved, remove spoon or spatula and reduce heat to medium-high (or medium-low if you aren’t using a thermometer).
Cook, without stirring, for 8 to 12 minutes (or longer if at a lower temperature) until the mixture reaches the color of golden caramel (the color of an older penny), about 340°F.
4 Add the baking soda: When the caramel has reached the right color/temperature, remove from heat and remove thermometer (if using).
Stir in the vanilla, baking soda, and salt carefully. The caramel will boil and steam.
5 Stir in the peanuts, then immediately pour onto the prepared baking sheet. Spread the brittle evenly across the pan using a heatproof spatula.
6 Cool and store: Let the brittle cool for 1 hour at room temperature, and then break the brittle into 2-inch pieces with your hands or chop with a chef’s knife (I like using my hands; it’s more fun and safer as you have more control over the pieces you're breaking).