3 ½ ounces bittersweet chocolate, such as Valrhona Guanaja 70%, chopped 3 ½ ounces unsweetened chocolate, such as Scharffen Berger 99%, chopped
1 ¾ cups cake flour
1 ½ Tbs unsweetened cocoa powder
Pinch of salt
½ pound (2 sticks) unsalted butter, at room temperature
1 ¼ cups granulated sugar
4 large eggs, at room temperature
1 cup semisweet chocolate chips, such as Ghirardelli
Adjust a rack to the middle position, and preheat the oven to 375 degrees Fahrenheit. Grease a 12-well muffin pan or mini popover pan with butter or cooking spray.
In a heatproof bowl set over a pan of barely simmering water, melt the bittersweet and unsweetened chocolates together, stirring occasionally. When the chocolates are just melted, remove the bowl from the heat and set it aside.
Sift the flour, cocoa, and salt together into a medium bowl. Set it aside.
In the bowl of an electric mixer (or a mixing bowl), beat the butter and sugar until very light and fluffy. Add the eggs one at a time, mixing well after each addition. Beat in the melted chocolate until well incorporated. Using a rubber spatula or spoon, stir and fold in the dry ingredients in three additions. Add the chocolate chips and stir to combine. The batter will be quite thick.
Divide the batter between the wells of the muffin tin or popover pan. Bake the cakes for 15-18 minutes, or until they still feel quite soft in their centers when pressed lightly with your index finger. Do not overbake them, or they will be dry.
Remove the pan from the oven, and allow to cool on a rack for about 10 minutes. Carefully remove the cakes from the pan and cool completely before eating or storing.
