Make the chocolate ganache. Place finely chopped chocolate in a heatproof bowl and set aside. Add the cream to a small saucepan and heat just until it begins to simmer. Pour the heated cream over the chocolate and let it sit for 2 minutes before stirring with a rubber spatula until the chocolate is completely melted and the mixture is smooth and shiny. Set the ganache aside and allow it to cool to room temperature (about 30 minutes).
½ cup heavy cream, 4 ounces bittersweet chocolate baking bar,
In the bowl of a stand mixer using the paddle attachment (or in a large bowl using an electric hand mixer), beat butter, vanilla, and salt on medium-high speed until smooth.
1 ½ cups unsalted butter,, 1 Tablespoon vanilla extract, ¼ teaspoon fine sea salt
Add sugar and cocoa powder slowly, beating well on medium speed and scraping the bowl often. Mix until well blended.
2 cups confectioners’ sugar, 1 cup Dutch processed cocoa powder
Add ganache to the frosting and mix on medium speed until the frosting is light and fluffy.
Notes
Storage: This frosting can be stored in an airtight container in the fridge for up to 4 days. If you plan to refrigerate the frosting before using to decorate a dessert, let the frosting come to room temperature and briefly re-whip it with a stand mixer or electric hand mixer so that it's soft and fluffy before using. Cakes or other desserts that have been decorated with chocolate ganache buttercream can be stored on a covered cake plate or stand at room temperature for up to 2 days or in the fridge for up to 4 days.Since this frosting is so rich, I find myself using slightly less when frosting a cake compared to when I use classic buttercream frosting. Therefore I find 3 cups of this frosting to be enough for one 2 layer 9 inch cake.