To make the sauce, combine the sour cream, blue cheese, whole milk, garlic powder, onion powder and salt, in a medium bowl. Cover with plastic wrap and transfer to the refrigerator until serving. Preheat the oven to 450 degrees. Line a baking sheet with parchment or foil and set aside. In a medium bowl, add the whole milk, beer, all-purpose flour, garlic powder, onion powder, baking powder and salt; mix until everything is just combined, being sure to not over mix. Dip each cauliflower floret into the batter, allowing any excess to run off, and transfer to the baking sheet. Repeat dipping process until you've worked your way through all of the florets. Spray the tops of the florets with cooking spray; this will help with the crisp-factor. Transfer the baking sheet to the oven and bake for 15 to 20 minutes, until the tops are lightly golden brown. Meanwhile, in a medium saucepan, melt the butter and pour in the Buffalo wing sauce. Mix until combined. Remove the cauliflower from the oven and drizzle half of the sauce atop the florets. Return the cauliflower to the oven and bake for an additional 5 minutes. Using a pair of tongs, add the cauliflower florets to the saucepan with the buffalo mixture and gently toss, until all of the florets are completely coated in sauce. Transfer to a large plate and serve alongside the dipping sauce and freshly cut celery.