Blue Cheese Dressing or store-bought vegan blue cheese dressing, for dipping
To make the buffalo sauce: In a small saucepan, combine the hot sauce, butter, and brown sugar. Bring to a simmer over medium heat and cook for 2 to 4 minutes, or until the butter has melted and the sugar has dissolved. Remove from the heat and set aside.
To make the everything coating: In a small bowl, combine the garlic, onion, sesame seeds, and salt. Set aside.
To make the cauliflower bites: In a medium bowl, whisk together the flour, cornmeal, cornstarch, salt, and pepper. Slowly add the seltzer water, whisking until well combined and a thick batter has formed.
In a wok or large saucepan, pour 3 inches (7.5 cm) of canola oil. Heat the oil to 350°F (175°C) when tested with a candy thermometer or a drop of batter fries quickly and bubbles up to the top. Line a plate with paper towels.
Working in batches, transfer half the cauliflower florets into the batter; mix around until all the florets are fully coated. Using tongs, pick up a piece of cauliflower, allowing excess batter to drip off, and carefully transfer into the frying oil; repeat with the remaining battered pieces.
Fry in small batches for 4 to 6 minutes, or until golden brown. Use a slotted spoon to transfer the cauliflower to the paper towel–lined plate. Repeat until all of the cauliflower is fried.
In a large bowl, toss 1/4 of the fried cauliflower bites with 1/4 of the buffalo sauce and 2 teaspoons (10 ml) of the "everything" mixture (you get a more even coating if you do it in batches). Transfer the bites to a serving tray and repeat for the remaining bites. Sprinkle the plated cauliflower with any remaining everything coating and the scallions, if using.
Serve with blue cheese dressing on the side, for dipping.