Pour frying oil into a large dutch oven so that it fills about 1/3 of the way. Using a frying thermometer, heat the oil over medium heat until it reaches a temperature of 360 degrees F.
While the oil is heating up, prepare your fritter batter. In the bowl of your stand mixer, whisk together the flour, 1/3 cup sugar, brown sugar, baking powder, salt, 1 teaspoon cinnamon and nutmeg. With dough hook attached, set your stand mixer on low speed. Add the eggs, one at at a time, fully incorporating after each addition. Then add the milk, vanilla and melted butter. Knead until the dough is just mixed and no traces of flour remain. Do not over mix. Scrape down the sides of the bowl where needed. Set aside.
In a medium bowl, combine the diced apple and remaining 2 tablespoons sugar and 1 teaspoon cinnamon. Toss to evenly coat and then stir the apples into the fritter batter.
Once the oil is hot, drop a small amount of dough into the oil. If it browns and floats to the top, then the oil is ready. In 1-2 tablespoon increments (I used a melon baller), drop the dough into the hot oil, working in batches of 5 or 6. Do not over crowd the dutch oven and keep a close eye that the temperature stays just around 360. Once brown on all sides (about 2-3 minutes), remove the fritters from the hot oil with a spider spatula or something similar and transfer to a plate that has been lined with a paper towel. Repeat this step for the rest of your fritter batter.
Prepare the glaze by whisking the confectioner's sugar, whole milk, salt and vanilla extract in a shallow bowl. Add more milk if the glaze is too thick. Add more flour if the glaze is too thin. Dip the cinnamon apple fritters into the glaze and place on a sheet of parchment paper to harden slightly.
Enjoy warm with a glass of milk or a cup of coffee!