Instructions:
- Preheat oven to 375°F (190°C). Grease a 9x9 inch (or similar 2-quart) baking dish thoroughly with butter.
- Bring a large pot of salted water to a boil. Briefly plunge the sliced cabbage into the boiling water for 2–3 minutes until slightly tender. Drain very well and pat dry.
- Melt the 2 Tbsp butter for the sauce in a saucepan over medium heat. Whisk in the flour continuously for 1 minute to form a smooth roux.
- Gradually whisk in the milk and stock until smooth. Bring the mixture to a gentle simmer, whisking constantly, until it thickens enough to coat the back of a spoon (about 5–7 minutes).
- Remove the thickened sauce from the heat. Stir in the Dijon mustard, nutmeg, salt, pepper, and 1 cup of the grated Cheddar until fully melted and smooth. Taste and adjust seasoning.
- Assemble the bake: Layer half of the blanched cabbage into the prepared baking dish. Pour half of the cheese sauce over the top. Repeat with the remaining cabbage and sauce.
- In a small bowl, combine the Panko breadcrumbs, remaining grated Cheddar, and Parmesan (if using). Sprinkle evenly over the top layer of the bake.
- Bake for 35–40 minutes, or until the sauce is bubbling up around the sides and the topping is golden brown and crisp.
- Let the dish rest for 10 minutes before serving to allow the sauce to settle.