Mix all mug cake ingredients, then pour into a large mug that has been sprayed with non-stick cooking spray. Microwave for 2 minutes and 15 seconds. Your cooking time may vary slightly with the power of your microwave.
Mix coconut milk solids, collagen, and Stevia until smooth. Serve on top of a slightly cooled mug cake.
Notes
To get the coconut milk solids, refrigerate a can of Thai Kitchen full-fat coconut milk overnight. Flip the can upside down and open it from the bottom, then pour off the liquid. You'll be left with coconut milk solids.