Preheat oven to 350°. In a large bowl, beat eggs, sugar and vanilla on high until thick and lemon-colored, about 4 minutes. Combine flour, baking powder and salt; add to egg mixture. Beat on low just until combined. Heat milk and butter in a small saucepan until butter melts. Add to batter; beat thoroughly (the batter will be thin). Pour into a greased 9-in. square baking pan. Bake until cake tests done, 20-25 minutes. Cool slightly. For frosting, blend all ingredients well; spread over warm cake. Broil about 4 in. from the heat for 3-4 minutes or until the top is lightly browned.