Grab a 12 oz mug and generously spray the inside with baking spray to prevent sticking.
Place butter in the mug and microwave it for about 20-30 seconds or until it’s fully melted.
Add the brown sugar and vanilla to the mug with the melted butter. Whisk them together until well combined.
Crack an egg into the mug, then add the oats, baking powder, cinnamon, nutmeg, and a pinch of salt. Mix everything together until it’s nicely blended.
Stir in the milk until everything is smoothly incorporated.
Put the mug in the microwave and heat for 30 seconds. Then pause and stir the mixture to help it cook evenly.
Microwave for an additional 1 minute. Check if the cake is done—it should be set and slightly springy to the touch.
Let it cool for a minute or two before enjoying your freshly made oatmeal mug cake!
Notes
Whisk Thoroughly: Whisk the ingredients vigorously after adding each to break up clumps and incorporate air, making the cake lighter and fluffier.
Adjust Microwave Time: Microwaves vary in power, so start with the shorter cooking time and add more in short bursts if needed. This prevents overcooking, which can make the cake rubbery.
Add Toppings: Enhance your mug cake with toppings like a dollop of yogurt, a sprinkle of granola, fresh fruit, or a drizzle of honey or maple syrup right before serving for added flavor and texture.
Use a Tall Mug: Choose a tall mug to allow the cake room to rise without spilling over as it cooks.