Beets and skordalia, a potato-vinegar puree, are a classic Greek pair, even better with pan-seared black cod.
Make the skordalia: Bring potatoes and garlic to a boil in a medium pot of salted water. Reduce heat, and simmer 10 minutes. Drain, and let cool.
Peel garlic, and mash with potatoes. Pulse potatoes and vinegar in a food processor. Working quickly, add safflower oil in a steady stream, then club soda. Transfer to a bowl, and season with salt. Cover, and refrigerate.
Make the beets: Bring beets to a boil in a small pot of salted water. Reduce heat, and simmer until tender, about 25 minutes. Drain, let cool, peel, and cut into quarters. Heat olive oil in large saute pan over medium heat. Add garlic; cook until golden, about 2 minutes. Add beet greens, and cook, stirring, until wilted, about 3 minutes. Stir in beets. Season with salt and pepper.
Make the cod: Preheat oven to 375 degrees. Heat olive oil in an ovenproof skillet over high heat. Cook cod on 1 side until bottom is golden brown, about 5 minutes. Transfer skillet to oven, and roast until fish is opaque, 5 minutes. Serve, crisp side up, with skordalia, beets, and greens. Garnish with dill.