Cut cauliflower into florets about 1.5 inches each so they cook evenly.
In a large bowl, whisk together flour, milk, salt, and black pepper until the batter is smooth with no lumps.
Preheat the air fryer to 400°F for 3 minutes and line the basket with a parchment paper liner.
Dip each floret into the batter, let excess drip off, and place in a single layer in the basket without overlapping.
Air-fry at 400°F for 15 minutes total.
Shake the basket halfway through (at 7–8 minutes) and flip any stuck pieces with tongs for even browning.
In a separate bowl, stir together the hot sauce and melted butter.
When florets are golden and crisp, transfer them immediately to a large bowl.
Pour the buffalo sauce mixture over the hot cauliflower.
Toss gently until evenly coated and serve right away with ranch or blue cheese if desired.