2. Steam the beets for 12 to 15 minutes in a covered saucepan using a collapsible steamer. Set the beets aside to cool.
3. Put the walnuts on a baking sheet and bake them in the oven for 8 to 10 minutes or until fragrant and toasted.
4. Peel and quarter the cooked beets.
5. Wipe the outside of the endive with a damp cloth, trim the base and separate the leaves.
6. To make the vinaigrette, mix the vinegar, olive oil, salt & pepper together in a small bowl.
7. Just before serving, toss the mache or watercress with some of the sherry vinaigrette. Divide the greens among the 8 dinner-sized plates. Arrange the quartered beets and walnuts on top of the greens.