Caramel Apple Crumble Mug Cake

1. Prepare the Apple & Crumble Topping

1. In a small microwave-safe bowl, combine the diced apple with 1/2 teaspoon of brown sugar, a pinch of cinnamon, and a tiny splash of water. Microwave on high for 35–45 seconds until slightly softened and fragrant. Set aside.
2. In another small bowl, make the crumble topping: rub together 1 tablespoon of flour, 1 tablespoon of rolled oats, 1/2 tablespoon of brown sugar, a pinch of cinnamon, and 1 tablespoon of softened butter with your fingertips until clumpy and crumbly. Set aside.

2. Mix the Mug Cake Batter

1. In a large, microwave-safe mug (around 300–350ml capacity), whisk together the remaining 3 tablespoons of flour, the rest of the brown sugar, baking powder, remaining cinnamon, nutmeg, and a pinch of salt.
2. Add the milk, melted butter, and vanilla extract. Whisk thoroughly with a small fork or mini whisk until a smooth, thick batter forms, scraping the bottom edges so no dry flour remains.

3. Assemble and Microwave

1. Spoon the softened diced apples evenly over the batter, allowing a few pieces to sink in slightly.
2. Scatter the crumble mixture generously over the top of the apples.
3. Microwave on high (800–900W) for 70 to 90 seconds. The cake should puff up, feel set to a light touch in the center, and the crumble will look settled.

4. Finish and Serve

1. Let the mug cake rest for 2 minutes to allow the steam to settle and the sponge to finish setting.
2. Drizzle the warm caramel sauce generously over the top and enjoy straight from the mug with a spoon.