Preheat oven to 350F. Line an 8 x 4 inch baking loaf pan with parchment paper.
In a large bowl, add butter, eggs, sour cream, milk, vanilla. Whisk until evenly combined and smooth.
Add in almond flour, coconut flour, erythritol, baking powder. Whisk until batter is smooth.
Pour batter into prepared loaf pan. Bake for about 50-55 minutes or until cake is done.
While cake is cooling, make your icing. In a small bowl, combine all icing ingredients. Whisk until smooth. If needed, add a little more milk to thin out icing to your desired consistency. Drizzle onto cake once cooled. You should have enough icing to drizzle over the loaf. If you want to cover the surface of the loaf with icing you will need to double or triple the icing recipe.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.