Turn the oven to 400.
Make the honey-butter vinaigrette by melting the butter and let it cool slightly. Then stir it together with the honey, apple cider vinegar, salt and pepper.
If you haven't already done so, slice the spring onions (bulbs only, long green stems saved for another use) and the radishes in half.
Toss the radishes and onions in the vinaigrette, and then spread onto a rimmed baking sheet. Roast for 12 minutes, toss, and roast for 3 more minutes. If you'd like, you can toss in the radish greens here and they will wilt. Serve warm.