Pre-heat your oven to 425 degrees F.
Spread salt out on a quarter sheet tray. Spread out beets on the salt and bake for 60-75 minutes until they can be pierced with a skewer with zero resistance. Turn the beets every 20 minutes while baking.
Once beets are done, remove from oven and let sit for 5-10 minutes. Once cool enough to handle but still warm, peel the beets. Slice them into 2-3mm thick slices and organize them by size.
In a cast iron skillet, spread sugar around the pan in an even layer. Drizzle sherry vinegar around the sugar. Place pan over medium heat and allow sugar to caramelize without stirring. When sugar is light brown in colour, turn heat to low. Add 3 tbsp butter and stir over low heat for 90 seconds to 2 minutes.
Turn off heat and set pan aside momentarily until caramel stops bubbling. Carefully place beets around the pan in an overlapping spiral, keeping slices close together. Make outer ring with larger slices and smaller ring in middle with smaller slices. Season with fresh thyme leaves, salt and pepper.
