In a large glass measuring cup, melt butter. (I used a 2 cup Pyrex measuring cup.)

After butter is melted, add remaining ingredients (except sprinkles) to large glass measuring cup. Mix ingredients together thoroughly, making sure that flour is fully incorporated.

Mix in sprinkles (or other mix-ins)

Separate batter into two, 6 oz. mason jars. .

Place mason jars in microwave and cook 1.5 to 2.5 minutes, depending on your microwave. I did at least 2 minutes for mine.

CAREFULLY remove mason jars from microwave. They will be very hot.

Allow to cool completely prior to adding frosting. Top with additional sprinkles if desired.