Microwave on high for 1 minute 30 seconds (or 90 seconds).
For the Icing
Mix all ingredients together and drizzle over cake either inside the mug or pop cake out of mug onto plate.
Notes
Mind the Mug Size: Use a mug that is at least 16 ounces in size to allow for the cake to rise without overflowing during microwaving. Using a smaller mug may result in the batter spilling over and creating a mess in the microwave.
Check for Doneness: Microwave cooking times can vary depending on the wattage of your microwave oven. After microwaving the cake for the recommended time of 1 minute and 30 seconds, check the cake's doneness by inserting a toothpick into the center. If it comes out clean or with a few moist crumbs, the cake is ready. If not, microwave in 10-second intervals until done to avoid overcooking.
Customize Your Icing: Adjust the consistency of the icing to your liking by varying the amount of milk added. For a thicker icing, use less milk, and for a thinner drizzle, add more milk. Additionally, feel free to add a drop of food coloring to the icing for a pop of color or swap vanilla extract for other flavor extracts like almond or lemon for a different flavor profile.