I was having a serious craving for something sweet, but didn't want to make a huge amount of anything! I stumbled across the "mug cake" recipes, but all I had available was the King Arthur Gluten Free Flour mix I use when baking for my boss. So I tried it, and this worked beautifully! Now the Gluten Free folks can join in on the Mug Cake craze, and I can definitely tell you this was very yummy!
Using a 12 ounce microwave safe mug, soften 1 tablespoon butter in the microwave. Just 10 seconds. Stir in sugar until creamy, then add sour cream and just a few drops of vanilla extract. Mix well, then add the gluten free flour mix and the baking powder.
In a separate ramekin or small bowl, combine crumb topping ingredients. Mix with your fingers until it resembles coarse crumbs. Add the crumb topping to the mixture in the mug.
Start with 1 minute on high, adding 10 seconds and checking until it looks done to you. My microwave is 1100 watts, and it took 1 minute 20 seconds for this cake to cook. HERE IS THE IMPORTANT BIT! It's going to be very hot when you take it out of the microwave, so let the cake sit for a minute and cool down. Then go ahead and dig in!