In a large bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon.
In a separate bowl, whisk the eggs, milk, and melted butter until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Gently fold in the diced apples.
Heat the vegetable oil in a large, heavy-bottomed pot or Dutch oven over medium-high heat to about 350°F (175°C).
Carefully drop spoonfuls of batter into the hot oil, being careful not to overcrowd the pot. Fry for 2-3 minutes per side, until golden brown and cooked through.
Remove the fritters with a slotted spoon and place them on a wire rack set over paper towels to drain.
Serve warm, dusted with powdered sugar if desired.
Notes
These apple fritters are best enjoyed fresh, but leftovers can be stored in an airtight container at room temperature for up to two days.