ISO: Checkerboard Cake update & frosting recipe request

I'm happy to report that the checkerboard cake made it to town and was a hit at my Dad's 80th birthday party. The outside temperature reading was 122 when DH and I stacked and frosted the layers with the air conditioner blasting in the cab of our pickup in the parking lot of the restaurant. We dashed into the restaurant with it where the owner kindly offered to put it into his refrigerator without us even asking! Very nice of him. My Dad was pleasantly surprised by both the party and the cake. For the frosting I used the recipe from a package of semi sweet baking chocolate squares (I don't remember the brand), it was terrific, but I threw the package away! Does anyone have this recipe? It uses 8 of the semi sweet chocolate squares, 1 stick butter, 16 oz. powdered sugar, vanilla and milk. You melt the chocolate in the microwave. I'm hoping someone will post the recipe, it was very, very good frosting. -Micha