Heat oil in a deep dryer or Dutch oven to 375°F (175°C). Line a wire rack with paper towels.
In a small bowl, whisk flour, sugar, baking powder, salt, and cinnamon.
In a large bowl, whisk together milk, eggs, vanilla, and sourdough discard until light and foamy.
Add dry ingredients to the wet ingredients. Then fold in chopped apples. Stir gently until just combined.
Drop spoonfuls of batter (about 1/4 cup or 80g) into the hot oil. You will need to slightly spread out the dough after adding to the oil. Fry 2–3 at a time for about 2 minutes per side, or until deep golden brown.
Remove with a slotted spoon and let drain on the wire rack.
Whisk together glaze ingredients in a small bowl.
Dip warm fritters into glaze, coating both sides. Place on a wire rack with parchment paper underneath the rack.
Serve warm and enjoy!