Preheat oven to 450 F. Line a baking sheet with aluminum foil and spray with nonstick cooking spray.
Cut cauliflower into florets. Set aside.To cut a head of cauliflower - Beginning with the head of cauliflower right side up, cut it in half directly through the center. From each half, cut the cauliflower florets from the core, cutting at each individual stem.
In a medium bowl, combine flour, onion powder, garlic salt, and pepper. Whisk in the water.
Using gloved hands, coat each floret in flour mixture. Place coated florets on prepared baking sheet.
Bake for 20 minutes.
Meanwhile, make the Buffalo sauce by combining hot sauce and butter in a medium saucepan. Heat over medium-high until butter has melted.
Make a slurry from the cornstarch and 1/2 cup water. Pour slurry into saucepan and simmer until sauce begins to thicken.
When cauliflower is done, remove from oven and dip each floret into the buffalo sauce, turning to coat well. Put sauced florets back on pan and bake 10 more minutes.
Notes
Try to cut the florets into uniform pieces as well as you can, this way they will roast evenly in the oven.
I recommend using Frank red hot sauce, after all, it is this classic hot sauce that's combined with butter to create what we know as buffalo sauce. However, if you have a favorite hot sauce in mind, you can certainly use that instead.