Remove the greens from the beets and separately wash the roots and greens.
Roast or boil your beets.
To boil: slice the beet roots into ½-inch size pieces and place in a pot of salted water. Bring to a boil. Reduce the heat to a high simmer and cook until the beets are tender. About 25 minutes. Strain the beets and set aside.
To roast: either roast your beets whole (wrapped in foil at 400F until tender when pierced with a fork) and then sliced into ½ inch size pieces, or sliced into wedges and then roast at 375F, drizzled with olive oil, salt, and pepper until tender (30 minutes).
In a large cast iron pan over medium high heat add the butter. Once sizzling toss in the onion and cook, stirring often until beginning to soften and brown, about 5 minutes. Add the garlic, crushed red pepper flakes and salt. Cook, stirring often for about 1 minute longer. Add the beet greens and a small splash of water. Cook, stirring occasionally, until the greens begin to wilt and cook down. Once tender remove from the heat. Add the greens to a food processor and process until smooth. Drizzle in some freshly squeezed lemon juice or a dash of red wine vinegar. Taste for seasonings and adjust as needed.
Serve the beets on a plate drizzled with olive oil, flakey sea salt and the beet greens puree.