I had this recipe in my cake decorating box. I had it there for a couple of years until I found it recently. This is super easy to make and if you don't have a candy thermometer like me it's no big deal. It is so delicious and goes great with chocolate cake. This recipe is enough to cover an 8 inch cake 2 layer one. It goes on beautifully and smoothly.
In a sauce pan add water, sugar and corn syrup stir and let simmer until mixture reads 140 degrees in a candy thermometer. I don't have one so I do this by eye when the mixture starts to turn light golden brown. Melt chocolate in microwave and set aside.
While the mixture is cooking beat your egg whites until soft peaks. Add hot sugar mixture slowly to the egg whites while whisking at the same time. I don't have a stand mixer so I I use a hand one. The mixture will become fluffy like marshmallow cream about 5 minutes of mixing.
Cream together butter, salt and vanilla until smooth add fluffy mixture to the butter and start mixing. Add melted chocolate to the mixture and whisk until it comes together. You can store it in an air tight container in the fridge or on your counter. You should have no lumps and it should be smooth.