Preheat oven to 325º F. Use parchment paper liners to line a muffin tin. Set muffin pan aside.
Add the eggs, oil, yogurt, and vanilla to a large mixing bowl, and whisk to combine.
In a medium sized mixing bowl, add almond flour, collagen, coconut flour, monk fruit sweetener, baking powder, soda and sea salt. Mix to combine.
Add the dry ingredients into the bowl with the wet ingredients, and stir to combine into a thick batter.
*If adding mix-ins, fold them into the batter.
Scoop the batter into a muffin tin lined with parchment paper liners.
Optionally, make the pecan streusel. Add pecans, almond flour, monk fruit sweetener, and coconut oil or butter to a food processor, and pulse until a chunky topping is formed.
Add about 1/2 tablespoon of topping to the top of each muffin, slightly pressing in.
Bake the muffins for 22 minutes, or until the tops have just started to brown and the centers are fully cooked.
Allow to cool prior to serving.