I just found this on Pinterest and made it tonight, Wow, its a good one! It's like the Moulton lava cake but very simple. Its the One-Minute Chocolate Peanut butter mug cake. Almost too much for just one.

Moist chocolate cake with a molten peanut butter center bakes up in a microwaved mug in just one minute!

Ingredients

• 1/4 cup all-purpose flour
• 2 tablespoons unsweetened cocoa powder
• 2 tablespoons sugar
• 1/4 teaspoon baking powder
• 1/4 cup milk, at room temperature
• 2 tablespoons butter, melted and cooled
• 1/4 teaspoon pure vanilla extract
• 1 tablespoon creamy peanut butter
• 1 tablespoon mini chocolate chips

Instructions

1. In a small bowl, whisk together flour, cocoa powder, sugar,
   and baking powder until thoroughly, completely combined with no streaks
   of flour or cocoa powder remaining. Blend in milk, butter, and vanilla
   until batter is smooth. Pour batter into a 14-ounce (or larger)
   microwave-safe mug with straight sides.
2. Combine peanut butter and chocolate chips and dollop into the
   center of the mug, gently pressing down until even with the top of the
   batter. Microwave on high for 1 minute. Allow to cool for a couple of
   minutes before serving.

Notes

A tall, cylindrical mug with straight (not
angled) sides will ensure that the cake bakes evenly. I found a 14-ounce
mug to be the perfect size to allow the cake to rise up while baking
without overflowing. (I filled my mug to the top with water and then
transferred the water to a measuring cup to determine its capacity.) If
you use a smaller mug, you may want to bake the cake on top of a plate
or paper towel to catch any possible overflow.

The
strength of individual microwaves can vary. The first time you make this
recipe, be prepared to experiment a bit to make sure that 1 minute is
the perfect length of baking time. The nice thing about this cake is
that even if it is undercooked, you don't have to worry about raw eggs!

The mini chocolate chips are optional. So is the peanut butter, for that matter. But I don't recommend skipping either. ;)

As
an alternative to serving straight out of the mug, you may instead
spray the mug with non-stick cooking spray before adding the batter, and
then carefully overturn the cake onto a plate once baked.