Heat about 1 inch of vegetable oil in a large, deep skillet over medium-high heat. It's hot enough when a small piece of bread dropped in the oil turns golden brown in about 1 minute. Place the cauliflower slices in the batter to coat, letting any excess drip off, then place them in the hot oil. Do not crowd. Cook until golden brown on both sides, turning once, about 2 minutes per side. Transfer to paper towels to drain, then place in a baking pan and keep warm in the oven until all slices are fried. Serve hot.