Step 1

Preheat oven to 350°F. Coat an 8-inch-square baking dish with cooking spray. Melt 2 tablespoons butter in a large Dutch oven over medium-high heat. Add cabbage, onion and celery; stir to coat well. Cover and cook, stirring occasionally, until the cabbage is tender-crisp, 15 to 18 minutes.

Step 2

Meanwhile, place the remaining 1 tablespoon butter in a small microwaveable bowl; microwave on High until melted, about 20 seconds. Add crackers to the butter and toss together until combined.

Step 3

Sprinkle the cabbage mixture evenly with flour and stir to coat. Stir in milk and bring to a simmer over medium-high heat. Simmer, uncovered, stirring often, until the sauce is thickened and creamy and coats the cabbage mixture, 2 to 3 minutes. Add mustard, salt, cayenne, nutmeg and 1/2 cup cheese; stir until the cheese melts, about 30 seconds.

Step 4

Spoon the cabbage mixture into the prepared baking dish. Sprinkle evenly with the remaining 1/2 cup cheese and the buttered cracker mixture. Bake until bubbly around the edges and golden brown on top, about 20 minutes. Let stand for 5 minutes before serving.