For assembled-but-unbaked casseroles, prepare the casserole in a freezer-safe baking dish, but stop before baking. For cooked casseroles, cool completely before freezing.
Assembled, unbaked (best method for many casseroles): Assemble the casserole in a foil pan or a baking dish lined with foil (so you can remove the frozen block and free up your dish). Cover tightly with foil, then wrap in plastic wrap or place in a large freezer bag. When ready to cook, thaw in the refrigerator overnight and bake as directed, or bake from frozen at 25°F lower for 50% longer.
Fully cooked: Cool completely. Cover tightly and freeze. Thaw in the refrigerator and reheat at 350°F (175°C) until heated through (165°F / 74°C internal).
Individual portions: Cut a cooked casserole into portions, wrap each in plastic wrap and foil, and freeze. Individual portions reheat faster and reduce waste.
2 to 3 months.
Thaw in the refrigerator overnight. Bake or reheat as directed. If baking from frozen, add 50% more time and cover with foil to prevent the top from burning before the center heats through.