Combine first 3 ingredients in a large glass bowl. Mircowave 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 the next 4 ingredients (peanuts through vanilla).
Pour into a buttered 15- x 10-inch jellyroll pan; shake pan to spread thinly. Cool until firm, and break into pieces.
Melt the chocolate and dip peanut brittle pieces into melted chocolate. Place on wax paper, and let harden. Store in an airtight container.