Combine the peanut butter, powdered sugar, cocoa powder, espresso powder, and vanilla extract in a bowl. Mix until smooth and firm. Then, roll the mixture into small, bite-sized balls. Chill them in the refrigerator for 30 minutes. Once firm, dip and coat the balls in melted (ideally dark) chocolate. Sprinkle a pinch of sea salt on top before the chocolate sets. Chill again until the coating is solid, and dessert is served!