Preheat oven to 350. Spray a 9 inch round cake pan with cooking spray and line with parchment paper.
Spread the three tablespoons softened butter in the bottom of the lined cake pan. Sprinkle with the cinnamon and sweetener. Put the cranberries in a single layer on top.
Add all the cake ingredients to a large bowl and mix until smooth. Gently spread over the cranberries in the cake pan.
Bake on middle rack for 30-35 min until the center is set and the top is golden. Cool for 20 minutes. Run a knife around the edge of the cake pan and then invert into a serving platter. Carefully peel off the parchment. Serve immediately or store in the fridge.