To prepare the beets

1. Scrub the beets and rutabaga. Lop off the ends, and peel away the skin with a Y-Peeler or sharp knife.
2. Starting with the rutabaga, use a mandoline slicer and slice them all up. Place in one pile. Repeat the process with the golden beets, and finish with the red beets.
3. Place about 2 tablespoons of olive oil into the bottom of a 6.5-inch cast iron skillet.
4. Place alternating slices of beets in a straight line down the palm of your hand. I could fix about six at a time. Place them around the edge of the pan in a tight spiral. Keep working until the pan is filled. When you are done, go back and insert extra slices to make the arrangement tight. Once done, slightly press down on the top to make sure all of the slices are wedged in. Drizzle with more of the olive oil, season with some salt and pepper and set aside.
5. Preheat your oven to 400.
6. Once preheated, place the skillet into the oven to bake for an hour, checking on it every 15 minutes to ensure the tops are not burning. Drizzle again with a little more olive oil if any portions of the tops start to look singed.
7. Remove from the oven, drizzle with the balsamic vinegar and sprinkle with the fresh thyme. Bake for an additional 15 minutes.
8. Serve immediately straight out of the pan with crusty bread or focaccia and a glass of red wine.