Preheat the oven to Lightly wipe two 9-inch round cake pans with just a smidgen of coconut or other oil, then fit a round of parchment paper on the bottom of each pan. Combine the sweet potato, milk, cashews, lemon juice, and vanilla extract in a blender (or in a deep cup if using an immersion blender) and puree until completely smooth. In a large bowl, combine the flour, sugar, baking powder, baking soda, and sea salt. Add the wet ingredients to the dry (be sure to scrape out all the blended ingredients with a silicone spatula). Mix until well incorporated. Transfer to the prepared pans. Bake for 21–23 minutes, until the batter looks dry in the center and is set to the touch. Transfer to a wire rack to cool completely in the pans. Carefully invert the pans to remove the cakes and frost as desired. Makes 2 (9-inch) cake layers; serves 8