Preheat the oven to 350°F (177°C). Line a 12-count muffin pan with cupcake liners. Set aside.

Melt the butter and chocolate together in the microwave. Microwave in 30-second increments, stirring after each increment. 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 bowl, whisk 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 over-mix. 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.

When the cupcakes are nearly cool, melt the white chocolate for the frosting: Place chopped white chocolate in a microwave-safe bowl (I usually use a glass liquid measuring cup), and microwave in 20-second increments, stirring after every 20 seconds until completely smooth. Set it aside to cool at room temperature for 20 minutes. (Be sure the melted white chocolate has cooled for 20 minutes, so it’s still melted but not scorching hot, which would melt the butter.)

In a medium bowl using a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed for 1 minute. Switch the mixer to low speed and slowly add the confectioners’ sugar. Stir the cooled white chocolate so that it is smooth, and then add it to the butter/sugar mixture. Switch the mixer to medium speed and beat for 2 minutes until combined and creamy. Add the cream, vanilla extract, and salt. Beat for 1 minute until combined. Taste. Add 1 more Tablespoon of heavy cream/milk if needed to thin out, if desired. Add another pinch of salt if frosting is too sweet.

Frost the cupcakes and top with melted chocolate drizzle and chocolate sprinkles, if desired. I used a Wilton 1M piping tip in the pictured cupcakes.

Cover and store leftovers in the refrigerator for up to 4–5 days.