Wash, core, and thinly slice apple into ⅛ inch wedges. Transfer to a bowl and set aside.
In a medium bowl, whisk together eggs, water, salt, and pepper.
Heat a skillet over medium heat.
Chop bacon into smaller pieces.
Add bacon to skillet and cook, stirring occasionally, until crispy, 3-4 minutes. Transfer to a plate, leaving the grease in the skillet.
Preheat oven to broil and position rack about 4 inches from the top.
Grate ½ cup of cheddar. Add ½ to bowl with eggs and mix.
Once bacon has been transferred, add butter and apple slices to skillet. Stir to combine, and cook until apples are slightly softened, 1-2 minutes.
Return about ½ of the bacon to the skillet. Spread out the apples and bacon evenly.
Pour in egg mixture. As eggs set around the edge of the skillet, gently lift cooked portions with a spatula to allow uncooked egg to flow underneath. Cook until bottom and sides are firm but the top is still runny, 5-7 minutes.
Sprinkle remaining cheddar and bacon over top. Place skillet in the oven until the top is set, 2-3 minutes.
To serve, cut frittata into wedges and place on a plate. Enjoy!
