Whisk together the melted, cool butter, egg and lemon rind in a small bowl. Add the flour, almond, xylitol, baking powder, milk and juice. Stir well to combine.
Transfer the mixture into a 1 cup (240ml) sized heat proof mug and microwave on high for 2 minutes. Remove from the microwave and set aside for 30 seconds.
Top with the coconut yogurt and serve immediately.