How to Make It
Using a sharp knife, cut the skin and bitter white pith from grapefruits. Working over a medium bowl, cut in between the membranes to release sections, and cut sections in half. Squeeze juice from membranes into bowl.
Preheat oven to 375°. On a large sheet of heavy-duty aluminum foil, rub beets with olive oil and season with salt. Wrap beets in aluminum foil and place on a baking sheet. Roast until tender, about 50 minutes. Unwrap beets and let cool slightly, then rub skins off with paper towels. Cut beets into 1/4-inch wedges. Add to bowl with grapefruit. Season with salt and pepper and toss well. Transfer to platter.
In a small saucepan, warm honey and rosemary sprig over moderately low heat. Remove sprig, and drizzle rosemary honey over salad. Garnish with flaky sea salt.