Preparation Whisk together vinegar, mustard, pepper, and 1/2 teaspoon salt in a large bowl, then add 3 tablespoons oil in a slow stream, whisking until combined well. Cook onions with remaining 1/4 teaspoon salt in remaining 2 tablespoons oil in a 12-inch heavy skillet over moderate heat, stirring occasionally, until golden brown, 18 to 20 minutes. Add onions to dressing, then add beets and cheese, stirring gently to combine. Serve sprinkled with pine nuts.
Preparation Whisk together vinegar, mustard, pepper, and 1/2 teaspoon salt in a large bowl, then add 3 tablespoons oil in a slow stream, whisking until combined well. Cook onions with remaining 1/4 teaspoon salt in remaining 2 tablespoons oil in a 12-inch heavy skillet over moderate heat, stirring occasionally, until golden brown, 18 to 20 minutes. Add onions to dressing, then add beets and cheese, stirring gently to combine. Serve sprinkled with pine nuts.