Preheat oven to 350°F and coat an 8×4 loaf pan with nonstick spray, butter, or coconut oil. You can also add parchment paper to ensure the cake comes out properly.
Add all dry ingredients to a medium-sized bowl (almond flour, coconut flour, collagen, baking powder, sweetener, and salt). Whisk to combine.
In a large bowl or stand mixer, add eggs and vanilla. Beat on high for 1 minute until light and fluffy. Add in sour cream, melted butter, and milk. Beat on high for 30-45 seconds.
Slowly add dry ingredients to wet ingredients in 2 to 3 batches. Mix well until combined. Let sit for 2 minutes. Mix one more time at low speed.
Pour batter into prepared pan and bake for 50-60 minutes until tops and edges are golden brown and a toothpick comes out clean when poked through the center. Add additional baking time if needed.