Add the chocolate and butter to a microwave safe bowl. Heat in 30 second increments until melted and smooth, stirring between each. Set aside to cool slightly.
5 ounces quality dark chocolate, 9 Tablespoons unsalted butter
In a large mixing bowl with an electric mixer or a stand mixer fitted with the whisk attachment, beat the sugar and eggs until very fluffy and pale, about 5 minutes. When you lift the whisk out of the mixture it should leave a ribbon on top that slowly disappears.
3/4 cup granulated sugar, 2 large eggs
Whisk the chocolate into the egg mixture and beat until just combined.
Add the cocoa powder and salt and beat again until combined. Cover the batter and chill for 1 hour or overnight. If chilling longer than 2 hours, let the batter sit at room temperature to soften slightly before scooping.
1/3 cup Dutch processed cocoa, 1/2 teaspoon kosher salt
Preheat the oven to 350°F and line a large baking sheet with parchment paper.
Place the powdered sugar in a medium bowl. Use a medium cookie scoop (2 Tablespoons) to scoop the dough then roll it into a ball. Use wet hands if the dough is sticky. Roll the dough into the powdered sugar and arrnage on the prepared baking sheet.
1/2 cup powdered sugar
Bake in preheated oven until puffed up and crackly on top, 8-10 minutes. Cool slightly on baking sheet then transfer to a wire cooling rack to cool completely.