Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius) and line a 12-cup muffin tin with parchment paper liners.
In a large bowl, whisk together the almond flour, coconut flour, baking soda, sea salt, and cinnamon until no clumps remain.
In a separate medium bowl, whisk the eggs until light and frothy, then incorporate the maple syrup, melted coconut oil, liquid bacon fat, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir with a silicone spatula until a uniform batter forms.
Gently fold in the diced apples and half of the crumbled bacon bits.
Distribute the batter evenly among the 12 muffin cups, filling each approximately three-quarters full.
Top each muffin with the remaining crumbled bacon, pressing lightly to ensure adhesion to the batter.
Bake for 20 to 22 minutes, or until the tops are golden brown and a toothpick inserted into the center of a muffin comes out clean.
Remove from the oven and allow the muffins to rest in the tin for 10 minutes before transferring to a wire rack to cool completely.