In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, and salt until uniform.

In a separate bowl, combine the beaten egg, milk, melted butter, lemon zest, and lemon juice.

Gently fold the wet ingredients into the dry ingredients using a spatula until just combined; do not overmix.

Heat the vegetable oil in a heavy-bottomed pot or deep fryer to 375 degrees Fahrenheit (190 degrees Celsius).

Using a small scoop or tablespoon, carefully drop rounded portions of batter into the hot oil, frying 4 to 5 at a time to maintain oil temperature.

Fry for approximately 2 to 3 minutes, turning once, until the fritters are golden brown and cooked through.

Use a slotted spoon to transfer the fritters to a wire rack or paper-towel-lined plate to drain.

Sift powdered sugar over the warm fritters and serve immediately.