Bring butter to room temperature. When butter is at room temp preheat oven to 325ºF. If that setting isn't there use 300ºF and adjust baking time for longer.
Combine only these dry ingredients. Almond flour, coconut flour, salt and baking soda
Cream the butter and sweetener. Not long just enough to combine even. Which should take a medium speed for a minute or two. Then add in sour cream, heavy cream, lemon extract and liquid stevia
Mix in the dry ingredients then add in eggs. Afterward fold in lemon juice then transfer to 9x5 greased loaf pan
Place in preheated oven doing your first check around 25-30 minutes. If cake isn't done check every 5 minutes after that. Use toothpick test where you place a toothpick through the middle. If comes out clean with a few crumbs the cake is done. If wet cook longer.