Place beets in a large pot, and cover with cold water by 2 inches. Bring to a boil over high heat; add 2 teaspoons salt. Reduce heat slightly to maintain a rolling boil. Cook until tender, about 30 minutes. Drain, and let cool slightly. Trim stem ends, then peel beets using a paring knife or a vegetable peeler. Cut beets crosswise into 1/4-inch-thick slices. Arrange on a platter.
Whisk together vinegar, 1 1/4 teaspoons salt, and the pepper in a small bowl. Add oil in a slow, steady stream, whisking until emulsified. Pour vinaigrette over beets, and serve.