So here they are. You begin very simply, with fresh whole pearl onions. Drop them into boiling water and simmer them for three or four minutes. Drain them, run cold water over them, and then peel them by cutting off the root ends and squeezing the onion out of its skin. By this procedure you will probably squeeze the onion out of its first layer or two of flesh, as well. It looks and seems wasteful, but can hardly be helped.
Over the years I've learned a variety of ways to simplify the rest of the story. The best and richest way to prepare creamed onions is to make a standard cream sauce, based on a roux of equal parts melted butter and flour stirred into a bubbling paste, to which milk is added; stir and cook until the sauce is smooth. Proportions for this are easy to remember: 2 tablespoons each of butter and flour will need 1 cup of milk, 4 tablespoons each will need 2 cups of milk, and 5 tablespoons of each will need 3 cups. Once the sauce is done, you can put the onions to finish cooking in it -- they are done in about five more minutes -- and then leave them to stay hot on a back burner, until you are ready to serve them.
Or, if you have a gluten allergy problem, you can cook the onions in milk themselves,
and then when you are ready to serve, thicken the milk with a free form, GF (gluten-free) flour and water slurry. You can also simply sprinkle potato flour over the bubbling liquid, and stir it in until it dissolves. Keep on adding a little more potato flour until the cream is as thick as you want it. Both these methods serve the purpose, although these sauces don't cling to the onions as nicely as a traditional sauce does.
Salt and pepper and a dash of nutmeg are all that is needed to finish any of them.
Now you may move on to the rest of your dinner. Don't forget to give thanks, really.