I can't remember how mom used to make it. My sauce is bland and horrible. Serve on toast. A white sauce is pretty bland. I use some of the water drained off the albacore in the sauce, maybe half, and half milk.
Some people just use a cream soup, such as cream of mushroom, thinned slightly.
It would be salty though. Melt butter in saucepan over low heat. Blend in flour, salt, and dash white pepper. Add milk all at once. Cook quickly, stirring constantly, until mixture thickens and bubbles.