Whisk together the flour, granulated sugar, baking powder, salt, and cinnamon in a large bowl. In a separate bowl, whisk the eggs, whole milk, and vanilla extract until blended.

Pour the wet mixture into the dry ingredients and stir just until combined. Fold in the finely diced apples, taking care not to overmix the batter.

Heat 1 1/2–2 inches of neutral oil in a deep, heavy pan to 350°F (175°C). Use a thermometer when possible so the fritters cook through without becoming greasy or overly dark.

Drop approximately 1/4 cup of batter per fritter into the hot oil, working in batches and leaving space between pieces. Fry for about 2–3 minutes per side, turning once, until puffed and deep golden brown.

Transfer the cooked fritters to a wire rack or paper towels to drain. A wire rack is preferred because it allows excess oil to drip away while keeping the bottoms from becoming soggy.

Stir the powdered sugar, milk or water, vanilla, and optional lemon juice together until smooth. Drizzle the glaze over warm fritters or dip their tops into it, then let the glaze set for several minutes.