Coffee Cake in a Mug

Name: Coffee Cake in a Mug
Prep time: 5 min
Cook time: 5 min
Total time: 10 min
Cuisine: American
Ingredients: Cake; 3 tbsp. all-purpose flour; 2 tbsp. old-fashioned oats; 2 tsp. Swerve brown sugar substitute (or another 0-calorie brown sugar swap that measures 1:1 like sugar); 1/4 tsp. baking powder; 1/4 tsp. cinnamon; Dash salt; 1 tbsp. unsweetened applesauce; 1 tbsp. (about 1/2 large) egg white or fat-free liquid egg substitute; 1/2 tsp. vanilla extract; Topping; 2 tsp. light butter in a tub