Combine your apples and 1/2 teaspoon cinnamon in a bowl and toss until apples are coated with cinnamon. Set aside.
In a separate, large bowl, combine flour, sugars, baking powder, remaining 1/2 teaspoon of cinnamon, and salt in a large bowl and whisk until well-combined.
Crack your eggs in a separate bowl and use a whisk to beat until pale yellow and frothy (about 15 seconds). Add milk and vanilla extract and whisk together.
Slowly, while whisking, pour melted butter into wet ingredients and whisk until well-combined (mixture may look slightly curdled).
Pour wet ingredients into dry and use a spatula to fold ingredients together until about halfway combined. Add cinnamon coated apple pieces and continue to fold into batter until all ingredients are just combined.
Set the batter aside and fill a Dutch oven or large saucepan 2-3" deep with oil for frying. Fix a candy thermometer to the edge (make sure it is in the oil but not touching the bottom of the pan) and set your heat to medium-low. Oil will need to reach 360-365F (175-185C) before you can continue.
While oil is heating, prepare your glaze by whisking together sugar, apple cider (or substitute) and vanilla extract until smooth. Set aside.
Once oil has reached temperature, use a large spoon or an ice cream scoop (this is my preferred method) to scoop about 3 Tablespoons of batter and *carefully* drop into the oil. Repeat with 2 more scoops of batter and fry each for 60-75 seconds on each side, or until golden brown.
Use tongs to remove apple fritters to a paper-towel lined plate and allow to cool several minutes before dipping in glaze and transferring to a cooling rack to allow glaze to set. Be sure to allow the oil to return to the correct temperature before frying more fritters.
Apple fritters are best enjoyed warm the same day they are made for best quality.
*For me this was about 2 apples. I recommend using an apple you enjoy eating; I used Gala apples that are neither too sweet nor too tart (I didn't enjoy Granny Smith apples in this recipe)**I like to use apple cider because it imparts a subtle, apple-y flavor into the glaze, but if you don't already have any on hand water or milk will work well. If your glaze is still too thick after combining your ingredients, add additional liquid 1 teaspoon at a time until desired consistency is reached. If it is too thin, add additional powdered sugar 1 Tablespoon at a time until correct consistency is reached. If you don't feel like making a glaze, these could instead be dusted with powdered sugar or rolled in a mixture of cinnamon and sugar after frying.