Preheat: Preheat your oven to 350°F (175°C) and butter a bundt pan very generously.
Mix Dry: In a mixing bowl, whisk almond flour, coconut flour and baking powder.
Cream Butter & Sweetener: Using a separate bowl, cream together the butter and erythritol.
Add Wet Ingredients: Beat in eggs one at a time, followed by almond milk, vinegar and vanilla extract.
Stir: Slowly add the dry ingredients to the wet mixture, making sure it all is well mixed together into a batter.
Bake: Transfer batter to prepared pan and bake 40–45 minutes or until golden.
Make Glaze: In a saucepan, melt butter, erythritol and water then mix in vanilla.
Glaze Cake: Pour glaze evenly over the top of the cake, while still warm prick holes into cake.