Add your flour, sugar, cocoa powder, baking soda, and salt to the mug. Mix to combine.
Once mixed, make three small wells in the dry ingredients.
Pour the vinegar, vanilla, and oil into each of the wells. Pour water over the entire mixture.
Mix the wet into the dry ingredients until they are fully combined.
Microwave for 1 minute 40 seconds. Your microwave may need more or less time depending on the wattage. Start low and if it needs more time you can add it back in. Don't overcook it!
Add your strawberries, sugar, and vanilla to a saucepan. Bring to a boil and let it simmer for about 1 minute, stirring frequently. Remove from heat and allow it to cool slightly.
Add your strawberry sauce to the top of your cake. We like to top ours with additional chocolate pieces and a little powdered sugar.
Notes
Nutritional Information is for 1 mug cake and 2 tablespoons of strawberry topping