Preheat oven to 350 degrees. Prepare beets by trimming the stems down to 1/4 inch. (it's important to leave a portion of the stem attached during the roasting process to retain moisture and avoid excess bleeding of color). Wash the beets using a vegetable brush to remove any grit. Trim the bottom "tail" of the beets. Brush beets with olive oil, sprinkle with sea salt and sprigs of thyme. Wrap in foil, place on cookie sheet, and roast until tender when pierced with knife - about 1 1/2 hours. If possible, allow beets to cool in their foil packet. Peel beets and slice into rounds.

Meanwhile, trim leaves from stem, wash, and blanch in boiling water. Shock the greens in ice water, drain (using paper towel to squeeze excess moisture from leaves), chop and set aside.

To make vinaigrette, whisk together the lemon juice, mustard, olive oil, tarragon, red pepper, salt and pepper in a medium sized bowl. When ready to serve the salad, use a Japanese mandoline or chef's knife to shave celery into thin slices. Toss the celery and the chopped beet greens with half the vinaigrette. Toss the beet rounds with remaining vinaigrette. Divide greens mixture onto four salad plates, and top with equal portions of beets. Top each salad with a crumbling of chèvre cheese.