In a large Dutch oven, pour the oil to a depth of 2 inches; heat to 360 degrees F.

In a large bowl, combine the flour, sugar, cocoa, baking powder, baking soda, and salt.

In a small bowl, whisk together the sour cream, milk, and eggs. Add to the flour mixture, stirring to combine.

Turn the dough out onto a lightly floured surface. Roll to 3/4-inch thickness. Using a 3-inch round cutter, cut out the doughnuts. Using a 1-inch round cutter, cut out the center of each doughnut.

Fry the doughnuts, in batches, for 1 minute per side. Drain on paper towels.

In a small bowl, combine the white chocolate and 2 tablespoons heavy cream. Microwave on High in 30-second intervals, stirring between each, until the chocolate is melted and smooth (about 1 minute total). Drizzle over the doughnuts.

In a small bowl, combine the bittersweet chocolate and remaining 2 tablespoons heavy cream. Microwave on High in 30-second intervals, stirring between each, until the chocolate is melted and smooth (about 1 minute total). Drizzle over the doughnuts