01 - In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and cinnamon.
02 - In a separate bowl, whisk milk, eggs, melted butter, and vanilla extract until blended.
03 - Add wet mixture to dry ingredients and fold gently with a spatula until just combined without overmixing.
04 - Heat vegetable oil in a deep pot to 350°F (175°C) and prepare a plate lined with paper towels for draining.
05 - Using a small cookie scoop or two teaspoons, carefully drop tablespoon-sized portions of dough into hot oil in batches.
06 - Fry donut holes for 2 to 3 minutes, turning occasionally, until golden brown and cooked through.
07 - Remove with a slotted spoon and place on the prepared paper towels to drain excess oil.
08 - In a shallow bowl, combine granulated sugar and ground cinnamon for coating.
09 - Brush each warm donut hole lightly with melted butter, then roll in the cinnamon sugar mixture to coat evenly.
10 - Serve immediately while warm for best texture and flavor.