In a medium bowl, whisk together the coconut oil and coconut sugar until fully combined and slightly lightened in colour (you can also use electric beaters), about 3-4 minutes. Whisk in the eggs until incorporated, then add the milk, vinegar, and vanilla. Stir to fully combine.
60 grams coconut oil, 100 grams coconut sugar, 2 large eggs, 120 ml non-dairy milk, 1 teaspoon apple cider vinegar, 1 teaspoon pure vanilla extract*
Add the milk mixture to the larger bowl and whisk gently until just combined. Don't over-mix, spelt is sensitive.
Pour the batter into the prepared pan, then top with the rhubarb in a spiral shape.
2-3 stalks rhubarb
Bake for 35-40 minutes, or until golden and a toothpick inserted in the centre of the cakes comes out clean. Cool for ten minutes in the pan before removing the sides and cooling completely on a rack.
Notes
* Vanilla can be substituted for here with a 1/4 teaspoon of cardamom instead.