From America's Test Kitchen Season 3: American Casseroles
Overcooking is the inevitable fate of many casseroles, as the contents are usually cooked twice: once on their own and once again when joined with the other casserole ingredients. We wanted a casserole with a silky sauce, a generous portion of turkey meat, and noodles cooked just till done.
We found we could cut the second cooking down to just 15 minutes by baking the recipe in a shallow dish that would allow it to heat through quickly. Most recipes for turkey Tetrazzini call for a béchamel sauce, in which milk is added to a roux (a paste made from fat and flour that is then cooked on the stovetop). In switching to a velouté, which is based on chicken stock rather than milk, we brightened up the texture and the flavor. We also used less sauce than most recipes call for, giving the other ingredients a chance to express themselves. Still looking for brighter flavor, we spruced things up with a shot of sherry and a little lemon juice and nutmeg. Parmesan cheese provided tang and bite, and a full 2 teaspoons of fresh thyme helped to freshen the overall impression of the dish.
Tetrazzini is also great with leftover chicken. Using a shallow baking dish without a cover and a very hot oven benefits both texture and flavor. Don’t skimp on the salt and pepper; this dish needs aggressive seasoning.