In a large bowl, whisk together the all-purpose flour, baking powder, salt, and sugar until well combined.

In a separate bowl, mix milk, beaten egg, and vanilla extract. Gradually combine wet ingredients with dry ingredients, stirring gently until just incorporated.

Carefully fold in the diced pineapple into the batter, ensuring not to crush the pieces.

Heat a non-stick skillet over medium heat and add butter to melt.

Drop spoonfuls of batter into the hot skillet, flattening slightly. Fry for about 2-3 minutes until golden, then flip and cook for another 2-3 minutes.

Transfer cooked fritters to a plate lined with paper towels to drain excess oil.

Gently toss warm fritters in the cinnamon sugar mixture to coat.