Spread peanut butter onto the cut side of the banana halves, and seal the halves back together. Slice into coins, and set aside.
In a saucepan over low heat, whisk together the egg yolks and 1/2 cup of the sugar. Stir in the vinegar and butter. Cook, whisking constantly until clear. Whisk in remaining sugar if you like.
Place the bananas into a serving bowl, and pour the sauce over them. This dish may be served hot or cold.
