Preheat oven to 325F. Grease a 7”x10” or an 8”x8” baking dish with lard, coconut oil, or ghee.
Add lard, honey and egg to the bowl of a standing mixer. With whisk attachment at medium speed, cream together until light and fluffy, about 3-4 minutes.
Meanwhile, combine apple cider vinegar and coconut cream (tip: add vinegar to the bottom of a measuring cup and then pour in cream to the ¾ cup line). Add 1 tsp baking soda and let sit for 2 minutes. (Caution: it will froth and expand, so use at least a 2 cup size measuring cup or do this step in a mixing bowl.)
Combine flour, spices, remaining baking soda and salt.
With mixer on low, add thirds of flour mixture and cream mixture, alternately. Once fully incorporated, remove whisk attachment and fold in rhubarb by hand.
Pour batter into prepared baking dish.
Make the crumb topping. Combine butter, sugar, cinnamon and flour in a small bowl. With your fingers, gently drop crumbs onto the surface of the cake batter, breaking up any bigger pieces as you go.
Sprinkle chopped pecans over the top of the cake, if using.
Put in the oven. Set a timer for 10 minutes.
After 10 minutes, increase oven temperature to 350F. Cook for a further 50 minutes.
Remove from oven and let cool before serving.