Heat about 1 inch of vegetable oil in a deep skillet or frying pan over medium heat until it reaches 350°F.

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

In another bowl, beat the egg and then add the milk and vanilla extract, mixing until well combined.

Pour the wet ingredients into the dry ingredients and stir until just combined; do not overmix.

Dip each pineapple ring into the batter, allowing any excess to drip off.

Carefully place the battered pineapple rings into the hot oil, frying in batches to avoid overcrowding. Fry for about 2-3 minutes on each side or until golden brown.

Remove the fried rings with a slotted spoon and place them on a paper towel-lined plate to drain excess oil.

If desired, dust with powdered sugar before serving.