Tiger Butter
rec.food.recipes/Christi Wilson/1995

1 pound white chocolate
1/2 cup chunky peanut butter
6 ounces (1 cup) semisweet chocolate morsels

Line a 15 1/2-by-10 1/2-inch jellyroll pan with wax paper. Break white chocolate into 1-inch pieces in a 1 1/2-quart microwave safe bowl. Microwave on high (100 percent power) 1 to 2 minutes or until melted. Stir until smooth. Add peanut butter and microwave on high for 2 minutes, or until melted; stir until smooth. (Microwave an additional 30 seconds if needed.) Spread mixture into prepared pan.

In a 2-cup microwave measuring cup, melt chocolate morsels on high for 1 to 2 minutes. Pour melted chocolate over peanut butter mixture; swirl through with a knife or drizzle melted chocolate on top of mixture using fine tip of pastry tube to make stripes. Refrigerate. When firm, cut or break into pieces. Store in refrigerator. Makes about 2 pounds, about 32 servings.

You could also use a double boiler to melt chocolates.

Another Tiger Butter recipe useing different amounts of the ingredients:
2 lbs white chocolate
8 oz peanut butter
3 oz melted milk chocolate