3 pounds fresh sweet (English) peas in the shell (about 3 cups shelled)
4 cups vegetable or chicken stock
2 tablespoons butter
1/3 cup leeks, sliced (use the tender white part only)
5 fresh mint leaves (sliced)
1/2 teaspoon Sugar
  salt (to taste)
2 tablespoons fresh mint leaves (thinly sliced for garnish, optional)