To prepare ahead of time, complete all steps except for baking. Store Crab Au Gratin in the refrigerator or freezer. For a frozen Crab Au Gratin, allow it to defrost fully in refrigerator before baking. From the refrigerator, bake Crab Au Gratin at 350 degrees Fahrenheit until warmed through. Cook time will vary depending on depth of baking dish used, but expect roughly 20-30 minutes baking time.