Step 1: Butter large cookie sheet.

Step 2: In heavy saucepan over medium heat, bring sugar and water to a boil, stirring constantly until sugar is completely dissolved.

Step 3: Stir in peanuts. Set candy thermometer in place, and continue cooking, stirring frequently until temperature reaches 290°F, or hard-crack stage (when a small amount of mixture dropped into very cold water separates into hard and brittle threads), about 20 minutes.

Step 4: Remove saucepan from heat; stir in butter and baking soda; immediately pour onto cookie sheet, spreading with spatula. Cool until completely firm.

Step 5: Break brittle into pieces. Stack on a plate. Store in tightly covered container.

{Makes about 1 pound}