Combine ¼ cup milk and flour in a saucepan whisk until well combined and cook for a couple of minutes. Stir in remaining ¾ cup milk and salt. Bring to a boil over medium heat, stirring frequently. Reduce the heat to low and simmer 2 minutes or until slightly thickened, stirring constantly. Once thickened, remove it from heat. Stir in the cheese and pepper, whisking until cheese melts.
Place cauliflower in a baking dish and cover with cheese sauce. Place in the oven for about 15 minutes or until golden brown and bubbly.