Roast Beef Tenderloin with Caramelized Onion and Mushroom Stuffing

From America's Test Kitchen Season 8: Holiday Beef Tenderloin Dinner

Beef tenderloin is perfect holiday fare. Add a rich stuffing and you’ve got the ultimate main course—at least in theory. We found three problems with stuffed tenderloin. The tenderloin’s thin, tapered shape made for uneven cooking; in the time it took to develop a nice crust, the meat overcooked; and “deluxe” fillings such as lobster and chanterelles were so chunky they fell out of the meat when sliced. We wanted a stuffed beef tenderloin with a deeply charred crust, a tender, rosy-pink interior, and an intensely flavored stuffing that stayed neatly rolled in the meat.

We had determined for our Roast Beef Tenderloin recipe (see page 109) that a center-cut tenderloin cooks more evenly than a whole one, and its cylindrical shape had an added advantage here as it made the roast easier to stuff. But making a slit in the roast didn’t give us much room for stuffing; double-butterflying the meat, to open it up like a book, gave us more space. After we stuffed, rolled, and tied it, we rubbed the roast with salt, pepper, and olive oil, which added flavor and helped develop a good crust when we seared the meat. We could fit just a cupful of stuffing in the meat, so we knew the flavors had to be intense. Chunky stuffings fell out when the roast was sliced, and anything with bread in it became a sponge that soaked up the meat juice. We finally decided on woodsy cremini mushrooms and caramelized onions, seasoned with Madeira and garlic; this combination made a savory-sweet jamlike filling that spread easily on the meat and held together well. Baby spinach added color and freshness. This roast was juicy and flavorful, and the filling was the ultimate touch of luxury.