4 ounces (120 grams) unsweetened chocolate, chopped
1/2 cup (113 grams) unsalted butter, cut into pieces
1 1/4 cup (250 grams) granulated white sugar
1 teaspoon pure vanilla extract
3 large eggs
3/4 cup (105 grams) all purpose flour
1/4 teaspoon salt
4 ounces (120 grams) semi-sweet or bittersweet chocolate, chopped
6 tablespoons (3 ounces) (84 grams) unsalted butter, cut in pieces
3/4 teaspoon pure vanilla extract2 teaspoons light corn syrup
1 1/3 cups (155 grams) confectioners (powdered or icing) sugar, sifted
1/2 cup sour cream, room temperature
1 teaspoon hot water
Preheat oven to 325 degrees F (170 degrees C) and place rack in center of oven. Line 12 muffin tins with paper or foil baking cups.
Melt the chopped chocolate and butter in a stainless steel bowl placed over a saucepan of simmering water. Once the chocolate is melted and smooth, remove from heat and let cool for a few minutes. Then stir (can also use a hand mixer) in the sugar. Add the vanilla and then add the eggs, one at a time, mixing well after each addition. Mix in the flour and salt until well blended.
Evenly divide the batter between the muffin cups. Place in the preheated oven and bake for about 20 minutes or until a toothpick inserted in the center of the cupcake has moist crumbs. Remove from oven and let cool on a wire rack.
To make Chocolate Frosting: Melt the chocolate and butter in a heatproof bowl placed over a saucepan of simmering water. Remove from heat and stir in the vanilla and corn syrup. Whisk in the sugar, a little at a time (at this point the frosting will be quite thick). Place the frosting in the bowl of your food processor and, with the processor running, gradually add the sour cream and hot water. Process until the frosting is nice and shiny. At this point you can simply spread some frosting on the top of each cupcake. However, if you want to pipe the frosting on top of the cupcakes you may have to place the frosting in the fridge for it to firm up. Periodically check and stir the frosting until it is of the desired piping consistency.