1. In a large mixing bowl, put the softened butter/margarine and beat until light and fluffy.
2. In another bowl, transfer the butter and set it aside.
3. In a small saucepan, combine sugar, water, and corn syrup. Place the pan on flame and cook until the temperature of syrup reaches 240 degree when measured with candy thermometer.
4. Remove the syrup from heat and let it cool a bit, for about 20 seconds.
5. On double boiler, melt chocolate chips
6. In a large mixing bowl, combine egg, egg whites, and vanilla. Beat until well blended.
7. Pour sugar syrup gradually into the mixing bowl with egg, while beating constantly on low speed. Beat for another 10 minutes or until the mixture cools.
8. Slowly add whipped butter/margarine into the bowl. Keep beating constantly on low while adding butter. Continue to beat until light and fluffy. Scrape down the sides to mix evenly.
9. Into the melted chocolate add 1/3 of the butter egg mixture. Fold to combine.
10. Drop the remaining mixture and fold to blend well.
11. Spread buttercream frosting on cake and enjoy!