CHEESY BRUSSELS SPROUTS GRATIN

Steps:

• Position racks in upper and lower thirds of oven; preheat to 475°. Spread pancetta on a rimmed baking sheet and roast, tossing once halfway through, until lightly browned and fat is beginning to render, 6-8 minutes.
• Whisk cream and mustard in a large glass measuring cup. Remove gratin from oven, carefully pour in cream mixture, and sprinkle cheese over.
• Reduce oven temperature to 375°. Return gratin to bottom rack, then place sheet with walnuts on top rack. Roast, 8-10 minutes, and cream is thick, vigorously bubbling, and browned around the edges, 15-20 minutes. Let gratin cool 10 minutes.