Place chocolate chips in a medium-sized bowl.
Heat the cream, corn syrup and 1 stick (1/2 cup) butter on the stove until it JUST comes to a boil.
Pour the heated cream mixture over chocolate chips. Make sure the chips are all submerged.
Let stand 1 minute and stir in one direction until smooth.
SARAH SAYS: If the chips are not melting, gently warm the mixture briefly over a pot of previously simmered water, while stirring in one direction the whole time.
Set aside momentarily to cool to tepid or about 100 degrees F. Do not let harden.
In a mixer bowl, fitted with a paddle attachment, beat the butter until softened.
Add the powdered sugar. Starting on low speed and slowly increasing the mixer to medium, beat the butter and sugar until light and smooth.
Add in the cooled ganache and vanilla extract and beat until smooth and light.
NOTE: The frosting will be quite liquidy at first, but, as it reaches room temperature, it will become thick and spreadable.
Frost the cake while the ganache is at room temperature. If refrigerated, let the ganache buttercream sit at room temperature to warm before using.