If making frosting: Soften the cream cheese in the microwave, using a small microwave-safe bowl, for about 10 seconds. Mix in the remaining ingredients and whisk until smooth. Set aside.
Place the butter in a microwave-safe ¾-cup, 3-inch-wide ramekin. Melt it in the microwave.
Whisk in the pumpkin, stevia, vanilla, and cinnamon. Add the egg and whisk to incorporate.
Add the coconut flour and baking powder. Whisk until smooth, scraping the sides and bottom and making sure the batter is completely smooth, well incorporated, and free of lumps. Especially check the bottom of the ramekin to make sure there are no unmixed areas there.
Microwave the cake for about 90 seconds, just until a toothpick inserted in its center comes out clean.
Carefully remove the ramekin from the microwave. Use oven mitts - it will be hot. Place it on a heatproof cutting board.
Gently remove the cake from the ramekin. Run a knife around the edges and slide a small rubber spatula under the bottom if needed. Turn the cake upside down to allow the bottom to air out and prevent sogginess. Allow it to slightly cool.
Enjoy the cake as is, or frost it: slice it in half crosswise. Frost the center, then the top. If you have enough frosting, you can frost the sides as well, as shown in the video.
Cut the cake into two servings and enjoy!
When I don't frost the cake, I eat the whole thing! Nutrition info for an unfrosted cake: Calories 238, fat 18g, saturated fat 10g, sodium 218mg, carbs 10g, fiber 5g, sugars 10g, protein 8g.** A granulated sweetener in the frosting will feel grainy, so please use a powdered sweetener.