Melt butter and peanut butter together. Remove from heat and stir in vanilla. Add icing sugar and mix well. Fold in crisp rice. Form mixture into 1” balls and place in the fridge until set hard. Meanwhile, melt the chocolate and shortening together gently, just until smooth. Using a fork or toothpick, dip the chilled peanut butter balls in the chocolate and place them on a parchment-lined pan. Place pan in the fridge for cookies to set. Makes about 2 dozen balls.