Preheat stove to 400 degrees. Wrap beets firmly in material lined foil. Cook on a baking sheet until delicate, around 60 minutes, 20 minutes. Let cool totally. Strip and cut across into 1/4-inch cuts.
Increment stove temperature to 425 degrees. Throw onion with 1 tablespoon oil and a big part of thyme. Season with salt and pepper and orchestrate in the lower part of a 3-quart round or oval gratin dish. On a cutting board, stack 1 cut every potato, beet, and tomato. Season with salt and pepper. Rehash with residual vegetables, keeping each stack independent. Move stacks to marginally dish and shingle to cover. Sprinkle with outstanding thyme and shower with 2 tablespoons oil. Cover firmly with material lined foil.
Prepare 30 minutes. Uncover; shower with staying 3 tablespoons oil. Prepare, uncovered, until vegetables are delicate and tomatoes are caramelized, around 35 minutes more. Let cool somewhat prior to serving.