Simple and rustic Italian soup.
Most home cooks dump every ingredient into a single pot and boil the dairy into submission, yielding a broken, greasy broth. Fat separates from liquid when overheated. Rendering the Italian sausage separately in a skillet controls this reaction. Drain excess grease before combining the meat with the broth. This prevents an oily slick on the surface.
Leaving the skins on the potatoes changes the starch behavior. Skins contain insoluble fiber that holds the potato quarters intact during boiling. Without skins, soft russets disintegrate into the broth completely. Cook the potato quarters in the chicken broth until a paring knife slides through the center with zero resistance, which usually takes about 15 minutes at a rolling boil.
Evaporated milk introduces heat-stable dairy solids. Regular milk curdles under high heat due to whey protein denaturation. Evaporated milk undergoes thermal processing that removes sixty percent of its water, concentrating the casein proteins. Simmer the combined soup for precisely 10 minutes to marry the flavors without scorching the dairy solids on the bottom of the vessel.
Substitutions alter the chemistry fundamentally. Replacing evaporated milk with heavy cream increases the fat content from roughly 8 grams of saturated fat to over 20 grams per serving, changing the emulsion stability entirely.