Prep Spiced Apples: In a medium bowl, toss diced apples with 2 tablespoons granulated sugar and 1 teaspoon cinnamon. Let sit for 10 minutes so apples release gentle juices and absorb spice.
Whisk Dry Ingredients: In a large mixing bowl, whisk together all-purpose flour, remaining granulated sugar, baking powder, remaining 1 teaspoon cinnamon, nutmeg, and sea salt until combined.
Combine Wet Ingredients: In a separate measuring jug, whisk whole eggs, milk, melted butter, and vanilla extract until smooth.
Fold Batter: Pour wet ingredients into dry ingredients, folding gently with a spatula just until barely combined (do not overmix). Gently fold in the macerated diced apples with any bowl juices until evenly distributed throughout the thick batter.
Heat Frying Oil: Pour oil into a heavy Dutch oven or deep skillet until 2 inches deep. Heat oil over medium heat until it registers 365°F (185°C) on a candy/oil thermometer.
Fry Fritters in Batches: Scoop 1/3-cup portions of batter and carefully drop into the hot oil, gently flattening slightly with the back of a spoon to create those iconic bakery craggy edges. Fry 2-3 fritters at a time for 2-3 minutes per side until deeply golden-brown and crisp. Remove with a slotted spider skimmer and drain on a wire cooling rack over a baking sheet.
Whisk Cider Glaze: In a shallow bowl, whisk powdered sugar, apple cider, and vanilla extract until completely smooth, glossy, and pourable.
Glaze & Set: While fritters are still warm, dunk each fritter entirely into the cider glaze or drizzle generously over top. Let rest on the wire rack for 5 minutes until the glaze sets into a delicate crackly shell. Serve warm!