Make the frosting: Place the cream cheese on a microwave-safe plate. Soften it in the microwave for about 10 seconds. Mix in the stevia and vanilla extract. Whisk with a small fork until smooth. Set aside.
Place the butter in a microwave-safe ¾-cup, 3.5-inch ramekin (the one I use is similar to this one). Melt it in the microwave in two 10-second sessions.
Using a small hand whisk or a fork, whisk in the stevia, vanilla, and egg until well incorporated.
Add the coconut flour. 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.
Mix in the cinnamon, followed by the baking powder.
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.
To frost the cake, slice it in half crosswise. Frost the center, then the top and sides, as shown in the video below.
Cut the cake into two servings and enjoy!
Video
Notes
After you add the coconut flour, the batter will be quite lumpy. It takes time and patience for the batter to become smooth, so just keep mixing. It takes a few minutes, but eventually, it WILL happen.You can keep the leftovers in the fridge, in an airtight container, for 2-3 days. Remove them from the fridge about 30 minutes before enjoying them.