Heat the oven to 350 degrees F. Cut the chard leaves from the stems. Chop the stems into short lengths, then cook briefly in boiling, lightly salted water until crisply tender. Remove the stems. Drip the leaves in the boiling water briefly, until they relax. Drain, let cool, and wring out the leaves. Spread the stems and leaves in a buttered shallow ovenproof dish.
Put the mustard in a bowl and stir in the cream and a grinding of salt and black pepper. Pour the seasoned cream over the stems and leaves, cover with grated Parmesan, and bake, 35 to 40 minutes, until the top has a light crust the color of honey.
Before starting Food52 with Merrill, I was a food writer and editor at the New York Times. I've written several books, including "Cooking for Mr. Latte" and "The Essential New York Times Cookbook." I played myself in "Julie & Julia" -- hope you didn't blink, or you may have missed the scene! I live in Brooklyn with my husband, Tad, and twins, Walker and Addison.