Line two large baking sheets with parchment.

In a 3-quart saucepan, combine sugar, corn syrup, and water. Place over medium-low heat and stir until sugar is dissolved and mixture comes to a boil.

Insert candy thermometer, increase heat to medium-high and boil, without stirring, until the temperature is 280°F.

Remove thermometer, lower the heat to medium, add butter, and stir vigorously until incorporated, about 30 seconds. Add peanuts and continue stirring about 2-3 minutes.

Insert thermometer, and cook, stirring occasionally, until temperature reaches 300°F. Remove from heat.

Add baking soda and stir in until candy foams up, about 30 seconds. Add vanilla and stir in.

Divide candy between prepared baking sheets and spread as thinly as possible.

As the candy cools, pull on the corners and sides to stretch the brittle, flipping the candy sheets over at least once to help stretch the center region.

Once cool, break into pieces and store in an airtight container.