Preheat oven to 425ºF. Place bacon in an unheated 10-inch cast iron skillet. Place over medium-low heat and cook until bacon is crisp and fat has rendered, 7 to 10 minutes. Transfer bacon to a cutting board; chop. Pour off all but 1 tablespoon bacon fat (reserve fat).
While bacon is cooking, combine almond flour, arrowroot, collagen, eggs, milk and 1 tablespoon maple syrup to a blender; blend until smooth. Add 1 tablespoon reserved bacon fat to blender; blend again.
After removing bacon from skillet, add apple. Sprinkle with a pinch of salt, drizzle with remaining 1 tablespoon maple syrup and cook, stirring occasionally, until apple begins to soften, 1 to 2 minutes.
Pour batter over apples in skillet. Sprinkle with chopped bacon. Transfer skillet to oven and cook until pancake is puffed and golden, 15 to 20 minutes. Let cool for 5 minutes before cutting and serving. (Pancake will deflate as it cools; that’s ok.) Pass additional maple syrup on the side.