Mix the flour and the buttermilk in a glass container and leave somewhere warm for 12-24 hours.
When ready to bake, preheat the oven and grease and flour two 8″ cake pans. (The batter will be quite acidic and start to act on the baking soda right away so you’ll want to work quickly once you mix the ingredients together.)
Cream the butter and sugar together. Mix in the eggs and vanilla.
Stir in the remaining flour, baking soda, baking powder, salt, and cinnamon. Then add the pre-fermented flour mix. Stir everything to mix well. Divide between the two cake pans.
Bake at 350 F for 25-35 min (until a toothpick comes out clean).
If using store-bought buttermilk for the recipe, make sure it was cultured (or it won’t preferment the flour).
To make the chocolate whip cream frosting, use 2 cups of whipped cream. (Use kefir cultured whipping cream for a probiotic kick!) Fold in 1/2 cup icing sugar, 5 Tbsp cocoa powder, 1 tsp vanilla, and a pinch of salt.