Preheat the oven to 350°F. Line muffin tin with cupcake liners.
In a medium mixing bowl, melt together butter and chopped unsweetened chocolate bar in 30-second increments, stirring between, until fully melted.
Stir granulated sugar and brown sugar into the chocolate mixture.
Add eggs and vanilla extract to the mixing bowl and stir to combine.
Add the flour to the batter and store until incorporated.
Fold in 1 cup of chocolate chips.
Divide the batter between 10 muffin cups.
Bake for 18 to 20 minutes or until a toothpick inserted into the brownies comes out with just a few crumbs.
Cool the brownie cupcakes completely.
When the cupcakes are cooled, prepare the ganache frosting.
Heat the heavy cream in a small saucepan or a microwave-safe container until steaming. Pour the cream over the chocolate chips in a large bowl. Cover with a plate for 2 to 3 minutes to contain the heat and allow the chocolate chips to soften.
Whisk until the mixture forms a smooth, glossy ganache. Cover with plastic wrap and refrigerate until the ganache is firm all the way through.
With a hand mixer, beat the firmed ganache until it is fluffy and forms stiff peaks.
Pipe frosting onto the cooled brownie cupcakes.