Begin by selecting a large microwave-safe mug and add the all-purpose flour, granulated sugar, baking powder, ground cinnamon, and a pinch of salt. Stir these dry ingredients together thoroughly to ensure even distribution.
Pour in the milk, vegetable oil, and vanilla extract. Using a fork or a small whisk, mix the ingredients until you achieve a smooth, lump-free batter. It's important to combine well to ensure the cake rises evenly.
In a separate small bowl, combine the brown sugar and the remaining 1/2 teaspoon of cinnamon to create a delightful filling. Sprinkle this mixture evenly across the top of your batter in the mug.
Taking a toothpick or a small fork, gently swirl the filling into the batter to mimic the classic cinnamon roll design. Be cautious not to overmix; a few visible swirls add to the charm of your cake!
Place the mug in the microwave and cook on high for approximately 1 minute to 1 minute and 30 seconds. Keep a close watch as cooking times can vary by microwave; the cake should puff up and feel set in the middle.
Once done, carefully remove the mug (it will be hot!) and allow the cake to cool for a minute or two. If you choose, drizzle some icing over the top for an extra sweet touch.
Notes
Serve warm with icing for a delightful indulgence.