This bright, peppery sauce goes well with a variety of proteins like chicken, fish or lamb, and can be served warm or cold. If serving warm, heat just before serving to preserve the bright green color. 

Preparation

Bring 2 quarts water and ½ teaspoon salt to a boil. Add garlic, return to a boil and cook for 30 seconds. Strain garlic and repeat the process 5-6 more times, or until the garlic is soft. 

In a separate pot, bring 4 quarts of water to a boil. Add watercress, cook for 30 seconds, then shock in an ice bath. When cold, drain the watercress and squeeze out any excess water. 

Place watercress, garlic, ½ teaspoon salt, pepper and lemon zest in a blender and puree on high. Slowly add the olive oil to emulsify and puree until smooth. 

Adjust seasoning with salt and pepper as needed.