In a mason jar or a glass container, add old-fashioned rolled oats, a pinch of salt, your milk of choice, and sweetener if desired.
Stir everything well using a spoon or fork. Make sure to mix from the bottom up—oats can settle and stick at the bottom.
Cover the container with a lid or seal tightly with plastic wrap or aluminum foil.
Refrigerate the oats for at least 2 hours, or overnight for the creamiest result. Store them on a shelf rather than the fridge door to avoid frequent changes of temperature.
Before serving, give the oats a good stir from bottom to top. Add your favorite toppings and dig in!