Easy Cauliflower Shepherd's Pie

Place oven rack 5 inches from broiler. Preheat the broiler (use "low" setting if you have it).

Microwave cauliflower according to package directions until softened. Stir in chives and pepper; set aside.

Meanwhile, heat a large cast-iron or other ovenproof skillet over medium-high heat (see Tip). Add beef and cook, stirring occasionally and breaking up the meat, until browned, 6 to 8 minutes; drain off most of the fat. Stir in Worcestershire and thyme, then add peas and carrots and onion; cook, stirring, until the vegetables are softened, about 5 minutes. Remove from heat.

Spread the cauliflower mixture evenly over the beef mixture and sprinkle with Cheddar. Broil just until the top is browned, about 3 minutes.