In a large pot, sweat the shallot. Add toasted chili flakes, fennel seeds, and garlic to pot. Deglaze with white wine and add Parmesan rind. Add milk and cream and bring to a simmer.
In a separate pan, make a roux with the butter and flour. Use roux to thicken the béchamel sauce as needed. Strain through a chinois. Cool and reserve until needed.
Cut cauliflower heads into florets and blanch. Combine cauliflower and béchamel sauce. Pour mixture into a prepared baking dish. Top with salt, white pepper, and Parmesan.
Bake at 350° until bubbly and the top is slightly brown.