To prepare a tenderstem broccoli mustard seeds and lemon recipe, you'll first need to prepare the broccoli. Cut the stems off of the stalks of broccoli and cut them into 12 inch (1.3 centimeters) lengths. Peel the outer leaves and slice them in half lengthwise. Toss the sliced broccoli with 2 tablespoons olive oil, 2 teaspoons kosher salt, and 1 tablespoon lemon juice. Season with salt and pepper to taste.