Preheat the oven to 375°F.
2. Put the beets in a bowl, drizzle with the oil, season with salt and pepper, and toss to coat the beets with the oil.
Transfer the beets to a roasting pan, spreading them out in a single layer, and roast in the oven until tender to a knife-tip, 15 to 20 minutes for very small; 45 minutes for very large.
Remove the pan from the oven and let the beets cool completely.3.
When cool enough to handle, slip the beets out of their skins, using paper towels to grasp them and a paring knife to help loosen the skin.
Discard the skins.
If using full-grown beets, quarter them or slice them into eighths.4.
Put the butter in a wide, heavy-bottomed sauté pan and melt it over medium-high heat.
Add the beets and honey and cook, stirring, until lightly caramelized, 4 to 6 minutes.
Add the sesame seeds and mint, shake and stir the pan to coat the beets evenly.
Drizzle lemon juice over the beets and season with salt and pepper.
Transfer the beets and all the juices and contents of the pan to a bowl and let cool slightly.5.
Add the watercress to the beets in the bowl and toss.
6. Divide the salad among 4 salad plates and serve.