Hello Claire! I completely understand your frustration with texture. A rubbery mug cake usually happens when the batter is either lacking sufficient liquid or gets overcooked in the microwave.
The sweet spot for a classic single-serving Oreo mug cake is a ratio of 4 standard Oreos to 3 tablespoons (about 45 ml) of milk. If you want a slightly larger treat, you can scale it up to 5 Oreos and 4 tablespoons (1/4 cup) of milk.
Here is the step-by-step method to ensure it turns out soft and cakey rather than dense or rubbery:
1. Place 4 Oreos directly into a microwave-safe mug and pour the 3 tablespoons of milk over them. Let them sit for about 30 to 45 seconds so the biscuits absorb the liquid and soften.
2. Use a fork to crush and whisk the Oreos thoroughly into the milk until you achieve a smooth, uniform batter with no dry lumps at the bottom.
3. As a small baker's tip, if you want an extra fluffy crumb, stir in 1/4 teaspoon of baking powder. It is optional, but it helps counteract the density of the crushed biscuits.
4. Microwave on high power for 60 to 70 seconds. Keep an eye on it around the 55-second mark because microwave wattages vary significantly. The cake is ready when the top looks matte and springy rather than wet.
5. Allow it to sit in the mug for 1 to 2 minutes before digging in. The residual heat finishes the bake and improves the final texture.
I hope this helps you get the perfect mug cake every time!
