Preheat the oven to 180 C (350 F). Grease an 8-inch pie dish or 6-inch cake tin.
In a medium bowl, whisk together the mashed pumpkin and yogurt until smooth. Whisk in the water, egg, cashew butter (or melted butter/coconut oil) and honey (or sugar). Add the flour and cornmeal to the bowl and stir until just combined. Quickly scrape all the batter into the prepared pan.
Bake for 25-30 minutes, until a toothpick inserted into the centre of the cake comes out clean.
Serve warm with butter and jam.