To a small microwave-safe bowl, add butter and microwave for 10-20 seconds until the butter is melted.
Add low-carb powdered sweetener, sour cream, heavy cream, and egg to the bowl with the melted butter and whisk until mixed well.
Add almond flour, coconut flour, baking soda, and salt and whisk until just combined.
Spray two, 4" ramekins with cooking spray, and divide the cake batter evenly between the two ramekins.
Microwave ramekins until cake is cooked through and springs back when lightly pressed with a finger. For best results, cook for 60 seconds** and check for doneness. Cook for additional 30 second increments until cake is fully cooked through. Be sure to watch cake so it does not overcook. Remove ramekins from microwave and allow to cool.
Wash the outside of the strawberries, and then, slice strawberries thinly.
If desired, remove cake from the ramekins and slice in half horizontally.
Top each cake with sliced strawberries and 2 tbsp of whipped cream, and serve!