In a small bowl, combine sliced apple, melted butter, 1/4 teaspoon of cinnamon, 1 teaspoon of brown sugar, and 1 teaspoon of flour. Mix until the apple slices are well-coated.

In another bowl, mix softened butter, 1 tablespoon of flour, oats, 1 tablespoon of brown sugar, and 1/4 teaspoon of cinnamon until crumbly.

Layer half of the apple filling at the bottom of a microwave-safe mug, followed by half of the crisp topping. Repeat the layers with remaining apple mixture and crisp topping.

Place the mug in the microwave and cook on high for about 3 minutes. Keep an eye on it to ensure it doesn’t overflow.

Once cooled slightly, serve warm. Top with whipped cream or vanilla ice cream if desired.