Line an 8 x 8-inch baking pan with a parchment sheet. Preheat the oven to 325°F (160°C).
In a small bowl, whisk together sifted flours, baking powder, and salt.
In a medium bowl, using an electric mixer, mix together creamy sunbutter, softened butter, sweetener, and baking soda.
Beat in the egg. Add vanilla and heavy cream (or almond milk) and whisk thoroughly.
Using a rubber spatula, stir in the flour mixture until just combined.
Put the batter in the prepared baking pan. Using your hands or a rubber spatula, smooth out the top. Optionally sprinkle with crushed almonds or walnuts.
Bake for 20 minutes or until a toothpick, inserted in the middle, comes out clean. Try not to over bake.
Remove from the pan and let it cool on a wire rack for about half an hour before cutting and serving.
Serve with some the desired kind of cream. Cheers!