Ingredients

• 2 large bunches watercress, thick stems trimmed
• 6 pounds russet potatoes, peeled, cut into 2-inch pieces
• 1 1/2 cups whole milk
• 1/2 cup (1 stick) butter
• 1/4 cup olive oil
• 2 bunches green onions, finely chopped (about 1 1/2 cups)

Instructions

1. Bring medium saucepan of water to boil. Add watercress and blanch 10 seconds. Drain. Pat dry and chop watercress.
2. Cook potatoes in large pot of boiling salted water until very tender, about 25 minutes. Drain. Return potatoes to pot. Stir over medium heat until any excess liquid evaporates, about 2 minutes.
3. Bring milk almost to simmer in small saucepan. Add hot milk, butter, and oil to potatoes; mash until almost smooth. (Can be prepared 2 hours ahead. Let stand uncovered at room temperature. Rewarm over medium-low heat, stirring often, before continuing.) Stir in green onions and watercress. Season with salt and pepper.