Combine first 3 ingredients in a large glass bowl. Microwave on HIGH 5 minutes, add peanuts, and microwave 2 more minutes with 1,000-watt microwave. Microwave 4 more minutes if using a 700-watt microwave. Stir in remaining ingredients.
Pour into a buttered 15- x 10-inch jellyroll pan; shake pan to spread thinly. Cool until firm, and break into pieces. Store in an airtight container.
Cooktop Brittle: Prep: 5 min., Cook: 8 min., Stand: 5 min. Cook first 3 ingredients in a medium-size heavy saucepan over medium heat, stirring constantly, until mixture starts to boil. Boil without stirring 5 minutes or until a candy thermometer reaches 310°. Add peanuts, and cook 2 to 3 more minutes or to 280°. (Mixture should be golden brown.) Remove from heat, and stir in butter and remaining ingredients. Pour mixture onto a metal surface or into a shallow pan. Allow to stand 5 minutes or until hardened. Break into pieces.
Pecan Brittle: Substitute 1 cup chopped pecans for peanuts.
Chocolate-Dipped Peanut Brittle: Prepare peanut brittle as directed. Melt 2 (2-ounce) chocolate bark coating squares; dip peanut brittle pieces into melted chocolate. Place on wax paper, and let harden
Popcorn Peanut Brittle: Prepare brittle as directed. Stir in 1 cup popped popcorn before pouring into pan.