01 - In a large mixing bowl, whisk together flour, sugar, baking powder, salt, and ground cinnamon until evenly combined.
02 - In a separate bowl, whisk together whole milk, eggs, melted butter, and vanilla extract until fully incorporated.
03 - Pour the wet ingredient mixture into the dry ingredients and fold together until just combined, being careful not to overmix.
04 - Heat 2 inches of vegetable oil in a deep saucepan to 350°F, monitoring the temperature with a thermometer.
05 - Using a small cookie scoop or two spoons, carefully drop tablespoon-sized balls of batter into the hot oil. Fry in batches, gently turning occasionally, until golden brown and fully cooked through, approximately 2 to 3 minutes per batch.
06 - Remove the fried donut holes using a slotted spoon and transfer to a paper towel-lined plate to drain excess oil.
07 - While the donut holes are still warm, roll them in the cinnamon sugar mixture until completely and evenly coated on all sides.
08 - Place chopped bittersweet chocolate and butter in a heatproof bowl. Heat the heavy cream in a small saucepan until it just begins to simmer, then pour over the chocolate and butter. Allow to sit undisturbed for 1 minute, then stir until smooth and glossy.
09 - Arrange warm cinnamon sugar-coated donut holes on a serving platter and present with the warm chocolate dipping sauce on the side.