Prepare your station.
Preheat the oven to 350° F / 175° C.
Line a muffin tin with 16 paper liners or spray with nonstick cooking spray.
Melt the chocolate.
In a small saucepan or a microwave-safe bowl, gently melt the chopped chocolate and butter together over low heat, stirring occasionally until smooth.
Set aside to cool to room temperature.
Whip the eggs.
In a large bowl using an electric mixer, beat the eggs and sugar together on medium-high speed for about 3-4 minutes, or until the mixture is pale, thick, and lemon-yellow.
Combine wet . Gently pour the cooled chocolate-butter mixture into the whipped eggs and sugar.
Stir with a spatula until just combined.
Add dry . Sift in the cake flour, baking powder, cocoa powder, and salt.
Beat on low speed for about 30 seconds, just until the streaks of flour disappear.
Do not overmix! Gently fold in the mini chocolate morsels with a spatula.
Fill and bake. Spoon the batter into the prepared muffin cups, filling each about two-thirds full.
Bake for 15 to 18 minutes. The cupcakes are done when a toothpick inserted into the center comes out with a few moist crumbs attached and the tops feel firm to the touch.
Let them cool in the pan for a few minutes before transferring to a wire rack to cool completely.
Using room temperature eggs is key! They whip up with the sugar to create a lighter, more voluminous batter, resulting in a superior crumb structure.
Don't overbake! The cupcakes are done when a toothpick comes out with a few moist crumbs attached, not perfectly clean. This ensures a moist, fudgy center.