Preheat oven to 350°F and butter a 9x13 inch baking dish.
Bring a large pot of salted water to a boil over high heat.
Add cauliflower pieces to the boiling water and blanch for 2 minutes.
Transfer the cauliflower to the prepared baking dish and let cool for about 5 minutes.
In a small skillet over medium-high heat, brown the pancetta.
Transfer the pancetta to a small bowl and set aside.
In the same skillet, melt the butter over medium heat.
Add the flour to the melted butter and stir until combined.
Continue stirring and cook for 2 minutes to cook the flour.
Remove the skillet from the heat and slowly add the milk, stirring continuously until smooth with no lumps.
Return the skillet to low heat and add the garlic clove and red pepper flakes.
Stir the sauce over low heat until it coats the back of a wooden spoon.
Add the Parmesan, salt, pepper, nutmeg, and reserved pancetta, then stir to combine.
Pour the sauce over the cauliflower to cover completely.
Sprinkle breadcrumbs evenly over the top.
Bake until the breadcrumbs are golden and the cauliflower is tender, about 25 minutes.
Serve immediately.
Notes
Tips and Tricks
Don't Overcook the Cauliflower - Blanching for just 2 minutes keeps the cauliflower firm enough to hold up during baking. Overcooking it will make the dish mushy.Stir the Roux Constantly - When cooking the flour and butter together, keep stirring to prevent burning. This step creates the base for a smooth sauce without lumps.Add Milk Slowly - Pour the milk into the roux gradually while stirring continuously. This technique prevents clumps and creates a silky texture.Grate Fresh Parmesan - Pre-grated Parmesan doesn't melt as smoothly as freshly grated cheese. Grate it yourself for the best sauce consistency.Use the Same Skillet - Cooking the pancetta first and then making the sauce in the same skillet saves dishes and adds extra flavor from the rendered fat.Watch the Breadcrumbs - Check the dish during the last 5 minutes of baking. If the breadcrumbs brown too quickly, cover loosely with foil to prevent burning.
Storing and Reheating
Refrigerate - Store leftovers in an airtight container in the refrigerator for up to 3 days.Freeze - Place cooled cauliflower in a freezer-safe container for up to 2 months. Thaw in the refrigerator overnight before reheating.Reheat in Oven - Transfer to a baking dish, cover with foil, and bake at 350°F for 15 to 20 minutes until heated through. Remove foil for the last 5 minutes to crisp the breadcrumbs.Reheat in Microwave - Place a portion in a microwave-safe dish, cover loosely, and heat in 1-minute intervals, stirring between each, until hot. The breadcrumbs won't stay as crispy with this method.