Heat the butter and 1 cup (170g) of the chocolate chips in a microwave safe bowl at 30 second intervals until melted (about 1 to 1½ min). Alternatively, melt the butter and chocolate chips in a 2 qt saucepan over medium-low heat, stirring constantly. Remove from heat.
Add the remaining ingredients (except for the rest of the chocolate chips) and stir until smooth. Do not overmix.
Stir in the remaining 1 cup of chocolate chips. Use a large cookie scoop to portion about ¼ cup of batter into 8 of the baking pan wells. Place the baking pans on a half sheet baking pan. Transfer to the oven.
Bake the brownies until the centers are set, about 20 to 25 minutes until a toothpick inserted in the center comes out clean or with a few crumbs attached.
Let brownies cool completely in the pan on a wire rack, then carefully remove them from the baking pans. You might need to loosen the sides with a lightly oiled table knife.
Make the ganache frosting: use a serrated knife to chop the chocolate into small pieces.
Warm the cream in a heavy-bottomed saucepan to just simmering (small bubbles...NOT boiling).
Put the chocolate in a heat-proof bowl. Pour the cream onto chocolate, cover and let sit for about 2 to 3 minutes, then start stirring. At first it will look grainy, but keep stirring until the mixture is smooth. Stir in the vanilla, then allow the ganache to cool to room temperature.
Use an immersion blender or a hand mixer to whip the ganache until it's thick, yet spreadable, and lightened in color, about 4 to 5 minutes.
When the brownie hearts are fully cooled, use a small offset spatula to spread the ganache frosting evenly over the top. Decorate with sprinkles if desired.
You can substitute other flavorings for the vanilla in the brownies and/or ganache. Try ¼ teaspoon of extracts like raspberry, mint, or Fiori di Sicilia (vanilla orange), or add a 1 to 2 tablespoons of bourbon, rum, or Kahlua for a boozy kick (just remember they'll be an adults-only treat then).For the ganache, you can choose your chocolate type: milk, semi sweet, or dark, depending on your preference...just make sure it's good quality.Instead of the mini heart baking pan, you can also use a 4-inch or smaller heart shaped cookie cutter to cut out the hearts if you prefer. Just bake the brownies in a 9- x 9-inch baking pan lined with parchment paper. After the brownies have cooled in the pan, turn them out onto a cutting board, peel away the parchment, then cut out as many hearts as you can.These brownies taste best at room temperature, and will keep in an airtight container for up to 3 days. For longer term storage, wrap them in wax paper, then foil and seal them in an airtight bag before freezing. They'll keep frozen for up to 3 months. Thaw at room temperature before serving.