In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt until well combined.
In a separate bowl, whisk the buttermilk, egg, and melted unsalted butter until smooth.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. Do not overmix; some lumps are okay.
Fold in the shredded cheddar cheese and shredded mozzarella cheese evenly into the batter.
Heat a non-stick skillet or griddle over medium heat and lightly grease it with vegetable oil.
Using a tablespoon, pour small dollops of batter onto the skillet to form bite-sized pancake poppers, about 1.5 inches in diameter.
Cook the pancake poppers for 2-3 minutes on the first side, until bubbles form on the surface and the edges look set.
Flip the poppers carefully and cook for another 2-3 minutes on the other side until golden brown and cooked through.
Remove the pancake poppers from the skillet and place them on a paper towel-lined plate to drain any excess oil.
Serve warm with maple syrup or your favorite breakfast dipping sauce.