I first made this icing while making eclairs for my final practicals in culinary school. It's my favorite icing/glaze to use when I make eclairs, cream puffs, & donuts as it sets up nicely and has a great shine to it.
Combine granulated sugar, corn syrup, water and salt in a saucepan. Bring to a boil, stirring to dissolve the sugar. Cook to 240°F. Wash the sides of the pan down with a clean pastry brush and hot water once the sugar comes to a boil.
While the sugar is cooking, combine the butter, confectioner’s sugar, and cocoa until evenly combined using a paddle attachment of electric mixer. * DO NOT OVER MIX - or will lose its shine.
~ With the mixer running at low speed, slowly pour the hot liquid into the cocoa mixture.
~ Add the vanilla and continue mixing until the icing is smooth, creamy and spreadable.
Variable: If necessary, thin the icing with a little hot water (DO THIS BY HAND). Icing may be re-heated for future use.