Mix the cornstarch (cornflour) with 2 tbsp of milk and set aside. Bring the rest of the milk to a simmer on the stove, but don’t let it boil and burn. Add the cornstarch slurry and stir well continuously.
The sauce should begin to thicken; keep stirring to avoid lumps. When it is your desired consistency, season well with salt and pepper.
Notes
A lot of these cheat’s white sauces should really be called cheat’s cheese sauce, as they are often cheese-based or will have cheese added in. But they are delicious and fit a range of purposes, from lasagne to cauliflower cheese.