When a recipe calls for one leek do you just use stalk?

No. A leek is a vegetable that typically consists of a long, cylindrical white stalk and a cluster of long, green leaves. When a recipe calls for one leek, it usually refers to the entire leek, including both the stalk and the leaves. However, some recipes may specify using only the stalk or only the leaves, so it's important to read the recipe carefully to determine which part of the leek is required.