SILVERTHORNE, Colo. — Tieghan Gerard was busy lighting pumpkin spice-scented candles when I arrived at her sunlit studio in October. After more than a year of negotiations with the representatives who guard her schedule and her image, she’d agreed to cook two recipes I’d chosen from the thousands on her immensely popular recipe site, Half Baked Harvest. Tieghan Gerard slices apples at her home in Silverthorne, Colo., Oct.