Cut the vanilla bean in half and scrape out the vanilla pulp with a knife.
Melt cocoa butter over low heat. Stir in cocoa powder and vanilla pulp. Sift powdered sugar over the top and stir in as well. Remove liquid chocolate from heat.
Season peanut butter with a little salt and pour a blob of peanut butter into each mold. Pour remaining chocolate over peanut butter. Place Peanut Butter Cups in the refrigerator to set completely.