For the Crepes:

1. In a large bowl, combine all ingredients and whisk vigorously until smooth.
2. In a large saucepan over medium heat, pour about 1/3-1/2 cup batter, covering the entire bottom of the pan in a thin layer.
3. Cook for about 2 minutes, or until the top looks mostly cooked too, even before flipping. Carefully (it will be thin and delicate) flip the crepe over, and cook for about 30 seconds.
4. Remove crepe from pan, and continue making crepes with remaining batter.

For the Filling:

1. Combine egg whites, sugar, and cream of tartar in a heat-proof bowl, ideally your mixing bowl.
2. Place over top of a large saucepan of simmering water, and whisk constantly for about 2 minutes, or until the sugar has dissolved and the egg whites are warm to the touch.
3. Immediately remove the bowl from heat, and place in your stand mixer. Start beating the egg white mixture slowly at first, but gradually increase speed to high.
4. Beat for 6-7 minutes, or until the mixture is glossy and thick.
5. Add vanilla, and beat until combined.
6. Add peanut butter, and beat until just blended.

For the Caramelized Bananas:

1. In a small bowl, whisk together brown sugar, water, and vanilla.
2. In a large saucepan over low heat, combine brown sugar mixture and bananas.
3. Cook for 3-4 minutes, gently stirring the bananas occasionally, until bananas are golden brown and soft, and the brown sugar mixture has caramelized.

To Serve:

1. Spoon or pipe the peanut butter marshmallow filling down the center of each crepe, divided evenly among the crepes.
2. Roll each crepe into about a 1-inch tube.
3. Spoon bananas evenly over each serving of 2-3 crepes.