Preheat the oven to 175°C degrees (350°F). Line a 12-cup cupcake/muffin pan with cupcake liners. Set aside.
Melt the butter and chocolate together in the microwave; in 30 second increments, stirring between each time. You may also melt the butter and chocolate over low heat on the stovetop. Stir until smooth and set aside to slightly cool.
In a medium sized bowl, toss the cocoa powder, flour, baking soda, baking powder, and salt together until thoroughly combined. Set aside.
In a large bowl, whisk the eggs, sugar, brown sugar, and vanilla together until smooth.
Add the cooled butter/chocolate and whisk until smooth. Add half of the flour mixture, then half of the buttermilk. Repeat until everything is added. Stir until *just* combined; do not overmix. The batter will be very thick like pudding.
Divide the batter between 12 liners in your cupcake pan. Bake for 18 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely before frosting.