Follow these simple, step-by-step instructions to achieve a perfect Microwave Pineapple Upside-Down Mug Cake in minutes. The key is to assemble the layers directly in the mug and to avoid overmixing the batter.

Step 1: Prepare the Topping

Begin by selecting a standard-sized, microwave-safe mug (approximately 12-14 ounces is ideal). There’s no need to grease it, as the melted butter in the topping will prevent the cake from sticking. Place the 1 tablespoon of melted unsalted butter directly into the bottom of the mug. Sprinkle the 1 tablespoon of packed brown sugar evenly over the melted butter. Use a small spoon or your fingertip to gently mix them together, ensuring the entire bottom of the mug is coated in this sweet, buttery mixture.

Step 2: Add the Fruit

Take your single pineapple ring and gently place it on top of the butter and brown sugar mixture in the mug. Press it down lightly so it sits flat. Next, place the maraschino cherry in the center hole of the pineapple ring. This creates the beautiful, classic “upside-down” presentation when you invert the cake later.

Step 3: Mix the Dry Ingredients

In a separate small bowl, combine all of the dry cake batter ingredients. Add the 4 tablespoons of all-purpose flour, 2 tablespoons of granulated sugar, 1/8 teaspoon of baking powder, and the pinch of salt. Whisk these ingredients together thoroughly with a fork or a small whisk. This step is crucial as it ensures the baking powder is evenly distributed, which will help the cake rise evenly and prevent any bitter clumps.

Step 4: Combine the Wet Ingredients and Make the Batter

Now, add the wet ingredients directly to the bowl with the mixed dry ingredients. Pour in the 3 tablespoons of milk, 1 tablespoon of vegetable oil, and 1/4 teaspoon of vanilla extract. Using your fork or whisk, mix everything together until just combined. Be careful not to overmix! A few small lumps in the batter are perfectly fine. Overmixing develops the gluten in the flour, which can lead to a tough or rubbery cake—the enemy of a good mug cake. The batter should be smooth but not overworked.

Step 5: Assemble and Cook

Gently pour the prepared cake batter into the mug, directly over the pineapple ring and cherry. Use a small spatula or the back of a spoon to spread the batter evenly, making sure it covers the fruit completely and reaches the edges of the mug. Place the mug in the center of your microwave.

Step 6: Microwave to Perfection

Microwave the cake on high power. The cooking time will vary depending on the wattage of your microwave. For a standard 1000-1200 watt microwave, start with 75-90 seconds. For a lower wattage microwave (700-900 watts), you may need closer to 2 minutes. The cake is done when the top looks set and springs back lightly when touched. A toothpick inserted into the center of the cake portion should come out clean or with a few moist crumbs attached.

Step 7: Rest and Serve

Carefully remove the mug from the microwave—it will be very hot! Let the cake rest for 1-2 minutes. This allows the cake to finish cooking from the residual heat and helps the caramelized topping to set slightly, making it easier to release. To serve, run a butter knife around the inside edge of the mug to loosen the cake. Place a small plate upside down over the top of the mug, and with confidence, swiftly flip them over together. Gently lift the mug away to reveal your beautiful, gooey-topped Pineapple Upside-Down Mug Cake.