Meanwhile, add 1 cup of the Merlot and the granulated sugar to a small saucepan over medium-high heat and stir until the sugar dissolves.
Bring to a boil, then reduce heat to a simmer until the mixture has reduced to a about 1/3 cup, about 25 minutes.
Allow the red wine reduction to completely cool in the fridge.
In an electric stand mixer fitted with a paddle attachment, cream butter until fluffy.
Gradually add confectioner's sugar a half cup at a time, beating until combined.
Add heavy cream and beat until light and fluffy for about 1-2 minutes.
Slowly add the cooled Merlot reduction and continue to beat the frosting until smooth.
Add the last 2 tablespoons of red wine one at a time and beat until smooth.
Add additional confectioner's sugar a 1/4 cup at a time if needed to reach desired frosting consistency.