Prepare and roast the cauliflower: Remove the stem leaves and core from the cauliflower and break off the florets into large chunks. (Not sure how to cut the cauliflower? Try my easy method details in the Cook's Noes above). If you like, you can cut away most of the stalks and just use the florets or use it stalks and all. Cut the florets into bite-sized pieces, but not too small.
Place the cauliflower in a large bowl. Drizzle with olive oil and season with salt and pepper. Scatter onto a baking sheet and roast in the preheated oven for 20-25 minutes, or until tender (test with a knife) and golden in spots. Remove from the oven, set aside and REDUCE THE OVEN TEMPERATURE TO 400F.
Prepare the cheese sauce: Measure out your milk and cream in a 2-cup measuring cup and set aside. Grate your cheese and have ready.
In a large saucepan (you'll be adding the cauliflower to it later, so make sure it's big enough), melt the butter oven medium heat. Add the flour and cook, stirring constantly for 2-3 minutes, or as long as you feel you can without letting it scorch. Reduce the heat under the pan to medium-low. Pour in a small amount of the cream/milk and whisk until a smooth paste forms. Add a bit more milk and whisk again until smooth. Add a bit more of the milk and whisk until smooth again. Add the remaining milk a bit at a time and whisk until smooth, until all the milk has been added. Cook sauce over medium-low heat and whisking regularly, until the sauce noticeably thickens. Remove the pot from the heat and stir in the grated cheese. Let stand without stirring for about 2 minutes, then stir together. The cheese should have all melted in to the sauce. If by chance it hasn't, you can return the pot to the burner over low heat to finish the melting. Add the nutmeg and stir in. Taste the sauce and add salt and freshly ground black pepper, as needed.
Add the roasted cauliflower to the pot with the cheese sauce and stir to completely coat the cauliflower. Spoon the cauliflower cheese mixture into a baking dish large enough to hold it all. Place the baking dish onto a baking sheet to catch any bubble overs.
Place into the preheated 400F and bake for 25-30 minutes, or until bubbly and deep golden on top. Let stand a few minutes before serving, to allow the sauce to set up a bit.
Notes
*If using heavy cream, you should be good with 3 Tbsp of flour. If using a lighter cream, whole milk or you're using cream, but want a thicker sauce, go with the 4 Tbsp of flour.** Heavy whipping cream will produce the best results, but if you prefer, you could use a lighter cream, such as table cream (18% b.f) or half and half cream (10% b.f.)Roast the cauliflower just until tender with just a few golden spots. Test it with a knife to be sure it's tender, then remove. You don't want to roast all of the moisture out of it.Add the milk/cream mixture in small increments (a scant 1/4 cup-ish at a time), to ensure a smooth sauce.Be sure to properly season your dish, starting with seasoning the cauliflower before roasting and ending with tasting and seasoning the cheese sauce at the end of cooking it on the stove-top, to really bring out the flavours.Turning off the heat under your pot (or removing it from the burner if you have an electric stovetop) immediately after adding the cheese helps to ensure a smooth and creamy sauce, as the cheese is allowed to melt slowly from the residual heat in the sauce.Be sure to read the “Ingredient and Cook's Notes" (above the recipe card!), where I share more detailed tips, variations and substitution suggestions for this recipe!