Whisk together the cashew butter, 1/4 cup pumpkin purée, 1/4 cup coconut sugar, and 1/2 tsp cinnamon until smooth. Add 1 tbsp or two of non-dairy milk, if needed, to thin. You don't want it runny, just spreadable. If you need to add milk or not will depend on how stiff your cashew butter is.
*It helps to start with room temperature ingredients, not straight from the refrigerator, so the coconut butter doesn't seize up. However, if it does, don't worry, just whisk it in the best you can. It will melt throughout the cake once in the oven.
This cake could serve anywhere from 10-18 people depending on how generous you want to be with the slices. There is a great post on The Cake Flake about how to cut a round cake several different ways. Nutrition facts were calculated assuming 14 servings.