To just add a little body to the stew (without lumps), soften the butter and mash 2 tablespoons of flour into the stew after it has heated. Stir until melted and blended. I don't bring it to a boil. Simmering works just as well.

The butter can be cut to 1/4 cup (1/2 stick) without hurting the flavor. Use half of the butter to thicken the stew as described above and use the other half to saute half a chopped onion (until clear but not browned) before adding the milk and salmon.

My mom use to fix this for me. I still enjoy the simplicity of the recipe. I eat it with chunks of sharp cheddar cheese and crushed saltines.