In a microwave-safe bowl, melt chocolate and butter (about 1 minute on high). Add in the peanut butter and whisk until everything is smooth. Mixture may need to be heated for additional time as needed. 10-15 seconds at a time.
Add in the powdered sugar, egg, egg yolk, flour, and vanilla. Stir until combined.
Grease 2 small baking dishes or ramekins and divide batter evenly between the two. Bake at 425°F for 13-15 minutes or until outside edge is firm, but the center is slightly soft.
Remove from oven and let stand a couple minutes before turning out onto a small plate. Top with powdered sugar, ice cream, caramel/chocolate sauce, and/or pecans. Serve warm.