Prep the Apples: In a medium bowl, combine 2 cups (250 g) diced granny smith apples with 1 tablespoon lemon juice, tossing to coat. Set aside.
Mix the Dry Ingredients: In another medium bowl, whisk together 1 ¼ cup (175 g) gluten-free flour, ¼ cup (50 g) granulated sugar, 2 tablespoons (16 g) cornstarch, 2 teaspoons baking powder, 1 teaspoon ground cinnamon, ¼ teaspoon nutmeg, and ½ teaspoon kosher salt until well combined. Set aside.
Prepare the Wet Ingredients: In a large bowl, whisk together 2 (100 g) large eggs, ¾ cup (183 g) whole milk, and 1 teaspoon vanilla extract until smooth.
Combine the Batter: Gradually add the dry ingredient mixture to the wet ingredients, stirring until a thick, smooth batter forms. Fold in the prepared apples, mixing until evenly distributed.
Heat the Oil: In a deep, heavy-bottomed pan or Dutch oven, add up to 6 cups (1,308 g) vegetable oil to a depth of 3-4 inches. Heat to 370-375°F (190°C), which takes about 10 minutes. Use a candy thermometer to monitor the temperature throughout frying.
Drop and Flatten the Batter: Working in batches of 3-4 fritters, use a large cookie scoop to drop spoonfuls of batter into the hot oil. Immediately use the back of the spoon to gently flatten each fritter. Don't overcrowd the pan or the oil temperature will drop and the fritters won't brown properly.
Fry Until Golden: Fry for 2-3 minutes per side, flipping halfway through, until golden brown and cooked through. The flattening in the previous step is critical for ensuring the centers cook completely.
Drain and Cool: Use a slotted spoon or spider spatula to transfer fritters to a wire rack set over a paper towel-lined baking sheet. Repeat the frying process with remaining batter.
Make the Glaze: In a small bowl, whisk together 1 cup (120 g) powdered sugar, ½ teaspoon vanilla extract, and 2 tablespoons apple cider or water until smooth.
Glaze the Fritters: Drizzle the glaze over the warm fritters or dip each fritter in the glaze, allowing any excess to drip off. Serve warm.