Orange juice and plum tomatoes brighten purply-red beets and balance out their earthy flavor.
Preheat oven to 375 degrees. Toss tomatoes with thyme, 1 teaspoon salt, and 1 tablespoon oil on a rimmed baking sheet. Spread in a single layer on half the sheet. Toss beets with 1 teaspoon salt and remaining 2 tablespoons oil. Wrap beets in parchment and then foil, and add to baking sheet. Roast until beets are tender, 45 to 50 minutes. Let cool slightly. Peel beets, and coarsely chop.
Puree tomatoes and beets in a food processor in 2 batches, then combine.
Just before serving, stir in orange juice, and season with salt.
Puree can be made up to 1 day ahead and refrigerated; reheat in a saucepan over low heat, stirring occasionally.