1/2 cup non-fat Real California sour cream or Greek-style yogurt
In a saucepan, bring milk and broth to a simmer and add potatoes. Cook, partially covered, about 10 minutes or until potatoes are tender. Add scallions and mint leaves; simmer for 5 minutes. Add peas and cook about 5 minutes or until peas are tender but still bright green. (If using frozen peas, cook 2 to 3 minutes or just until peas are soft.) Cool soup quickly in a larger pot of ice water to retain its color.
Purée in a blender or with an immersion blender until smooth.
Just before serving, heat soup over low heat and season with salt and white pepper. (To serve soup cold, place pot with blended soup in a larger pot of ice water and stir until cold, or place in refrigerator for several hours or overnight.) Ladle into bowls and garnish each serving with 1 tablespoon sour cream or yogurt.
Tip: Freeze soup in plastic containers or zip-closure bags; thaw in refrigerator and serve cold or heat over low heat, whisking until smooth.