Let's get to the heart of the matter here — the chocolate heart, that is! Use a cookie cutter to cut baked brownies into heart shapes, top with chocolate ganache, and you've got a Valentine's or other special-occasion dessert worth swooning over!
Preheat the oven to 350°F. Lightly grease a 9" x 13" pan. Line with parchment, and grease the parchment. While this step isn't strictly necessary, it makes getting the brownies out of the pan a whole lot easier.
To make the brownies: In a medium-sized microwave-safe bowl, or in a saucepan set over low heat, melt the butter, then add the sugar and stir to combine.
Return the mixture to the heat (or microwave) briefly, just until it's hot (about 110°F to 120°F), but not bubbling; it'll become shiny looking as you stir it. Heating this mixture a second time will dissolve more of the sugar, which will yield a shiny top crust on your brownies.
Stir in the cocoa, salt, baking powder, and vanilla.
Whisk in the eggs, stirring until smooth; then add the flour, chips, and espresso powder, again stirring until smooth.
Spoon the batter into the prepared pan.
Bake the brownies for 28 to 30 minutes, until a cake tester or toothpick inserted into the center comes out clean, or with just a few moist crumbs clinging to it. The brownies should feel set on the edges and in the center (barely).
Remove the brownies from the oven and cool them on a rack for 20 minutes before turning them out of the pan.
Loosen the edges; use a spatula or turner to loosen the bottom as much as possible; then flip the pan over onto another sheet of parchment or waxed paper. Peel the parchment off the bottom of the brownies. Let them cool completely.
Use a 2" heart cutter to cut 3 dozen hearts out of the brownies. (Or use a smaller or larger cutter to cut more or fewer hearts.) Place the hearts on a rack set over a piece of parchment or waxed paper.
Decide whether you want to drizzle the hearts with ganache, or coat them completely. You'll make the lesser amount of ganache for drizzling, the greater amount for glazing.
To make the ganache: Combine the chips, cream, and corn syrup in a microwave-safe bowl. Heat until the cream is very hot.
Stir the mixture until the chips melt, then drizzle over the brownie hearts, or spread to cover completely.
