Mix margarine, peanut butter and vanilla together. Add powdered sugar. Roll into balls. Chill for short time in the freezer or refrigerator. Melt bark for dipping in bowl. Insert toothpick into ball and dip in chocolate leaving an area exposed to resemble a "buckeye".
Place on waxed paper and continue. When completed go back and "touch" the hole with finger to close the hole. I usually keep these in the freezer until ready to use! The refrigerator will do fine as well.