Grease a rimmed cookie sheet with butter. Grease a spatula with butter. Set both aside.

Combine 2 cups sugar, ½ cup water and a pinch of salt in a medium saucepan. Cook over high heat, without stirring, about 3 minutes, until the sugar begins to melt and turn golden.

Continue to cook on high, stirring occasionally, until sugar melts completely and the mixture begins to turn a golden amber color. Watch carefully for the color after about 5 minutes.

Remove the saucepan from heat and stir in peanuts. Immediately pour the peanut mixture onto the buttered cookie sheet. Quickly spread the mixture over the baking sheet with the buttered metal spatula. Cool completely (about 15 minutes). The peanut brittle will have a glassy look when cooled. Break brittle into pieces.