Line a rimmed baking sheet with a nonstick baking mat or parchment paper.  Set aside.

Combine the sugar, water, butter, and corn syrup in a large saucepan.  Bring to a boil over moderately high heat.  Stir the mixture occasionally.  Continue to heat until the mixture turns a caramel color and is 300 degrees per a candy thermometer.

Working quickly, remove the mixture from the heat and stir in the baking soda (it will bubble up a bit).  Immediately stir in the nuts and pour the brittle onto your prepared baking sheet.  Press down the mixture into an even layer with the back of a large, oiled spoon.  Another option that works well is to cover the brittle with parchment paper and press the bottom of a heavy pan over the top.  This presses the brittle down quickly and with little mess. Sprinkle with salt, if desired.

Allow the brittle to cool completely, about 30 minutes.  Once the brittle has cooled, break into large chunks.  Store in an airtight container at room temperature for up to 1 month.  Enjoy!

Combine sugar, water, corn syrup, and butter to a large sauce pan.

Cook over moderately high heat until the mixture registers 300 degrees on a candy thermometer and is golden in color.

Remove from heat and carefully stir in the baking soda.

Quickly stir in the peanuts.

Pour the brittle onto a nonstick baking sheet and press down with the back of an oiled spoon or top with a sheet of parchment paper and use the bottom of a heavy pan to press down. You want a thin and level layer of brittle.

Allow to cool and then break into large pieces.