Averie Cooks

-1 Preheat oven to 425F. If you have a convection oven, now is a great time to use it.
-1 If desired for easier cleanup, line a baking sheet with foil. Spray the baking sheet (or the foil on top of it) with cooking spray and evenly scatter the cauliflower florets. Tip - Make sure they are all actually bite-sized which is practical for both eating them and so that they all cook evenly.
-1 Roasting Cauliflower - Evenly drizzle with olive oil, evenly sprinkle with seasoning salt, and toss with your hands to combine and coat evenly. Tips - I use 2 teaspoons seasoning salt because cauliflower needs a lot of help in the salt department and you are flavoring a very large amount of a bland vegetable, but of course, season to taste. If you don't keep seasoning salt on hand, then I would use 1 to 2 teaspoons kosher salt and 1 teaspoon freshly ground black pepper, or to taste.
-1 Roast for about 20 minutes, or until golden browned around the tips and edges, and tender. Depending on their size and your oven, they may be done 5 minutes early, or 5 minutes later, so keep a watchful eye and check on them early. If desired, you can flip and toss them once midway through roasting for even cooking. Tip - While the cauliflower roasts, move onto the next steps so the sauce is ready when the cauliflower is done.
-1 Cheese Sauce - To a medium saucepan, add the butter and heat over medium heat to melt, about 1 minute; stir constantly.
-1 Once melted, sprinkle the flour over the butter and cook for 1 minute, or until sand colored; whisk constantly. This is called making a roux. Tip - Do not shortchange this step because the finished dish will both taste awful from the raw flour and the cheese sauce will be thin and runny.
-1 Slowly add the milk, salt, thyme, optional nutmeg, and cook for about 3 minutes, or until thickened; whisk constantly to avoid lumps and ensure even thickening.
-1 Add the Gruyere cheese, half the Parmesan, and heat until the cheese melts; whisk constantly. Take off the heat and set aside once melted and combined.
-1 Assembly - To a 1.7-quart baking dish (or similar sized baking dish) that's sprayed with cooking spray, add the cauliflower and smooth it evenly.
-1 Evenly pour the cheese sauce over the top.
-1 In a small bowl, combine the the panko breadcrumbs, remaining Parmesan cheese, stir to combine. And evenly sprinkle this mixture over the top of the cheese sauce.
-1 Baking - Reduce the oven heat to 375F (if you are using convection, reduce the heat to 375F convection) and bake for about 20 minutes, or until the top is lightly golden browned or as desired.
-1 Serving- Optionally garnish with fresh herbs and serve.
-1 Storage - Extra gratin will keep airtight in the fridge for 5 days. Reheat gently in the microwave as desired. I don't recommend freezing this dish due to the cheese sauce and the texture of the cauliflower will also change during the freezing/thawing process.