Preheat oven to 350
Combine butter and erythritol in a large bowl. Add eggs, banana and vanilla and stir completely.
In a second bowl combine almond flour, baking soda and salt. Stir well and add to other bowl - mix to combine all ingredients.
Grease a jelly roll pan. Spread mixture evenly in pan and bake for 15 - 20 minutes. Remove when toothpick at center comes out clean. Let cool completely before removing.