Add remaining ingredients (except meatballs) and whisk until thickened.
Pour gravy over meatballs in casserole dish and bake at 350 for 1 hour and serve over butter noodles.
Building the Roux Foundation
Traditional brown gravies rely on pan drippings, but this style builds flavor from butter and flour cooked together. Melt three-quarters cup of butter completely before adding the flour. Whisk the flour continuously until the mixture turns smooth and bubbles actively. This cooking step removes the raw flour taste before the liquids enter the pan.
Controlling the Liquid Addition
Pouring six cups of beef stock into hot fat requires precision to avoid lumps. Add the stock gradually while whisking vigorously at medium heat. The starch molecules must hydrate evenly within the fat. Bring the liquid to a gentle simmer so the starches swell and thicken the sauce properly before dairy enters the equation.
Stabilizing the Dairy
Sour cream adds necessary acidity, but high heat causes dairy to curdle. Whisk the sour cream into the thickened stock off direct heat or over very low flames. Maintain a temperature below boiling once the sour cream is incorporated. Pour the finished gravy over the meatballs and bake at 350 degrees Fahrenheit for one hour.