Preheat Oven: Set to 350°F (175°C). Grease a loaf pan and line with parchment paper.
Mix Dry Ingredients: In a medium bowl, whisk together almond flour, coconut flour, baking powder, and salt.
Cream Butter & Sweetener: In a large bowl, beat butter and powdered erythritol until light and fluffy. Add eggs one at a time, mixing well after each. Stir in vanilla extract and zest, if using.
Combine: Add dry ingredients to wet ingredients in batches, alternating with almond milk. Mix until smooth and thick.
Bake: Pour batter into the prepared pan. Bake 45–55 minutes, or until a toothpick inserted in the center comes out clean. Let cool completely.
Make Glaze: Whisk powdered erythritol, heavy cream, and vanilla extract until smooth. Pour over cooled loaf and let set for at least 10 minutes.
Serving and Storage Tips:
