Directions

1. 1

   Make the sauce: Melt 1 1/2 tablespoons butter in a small heavy saucepan over medium heat. Whisk in the flour and cook, whisking constantly, for 2 minutes until it forms a light roux. Slowly add the beef broth in a thin stream while whisking continuously to avoid lumps. Bring to a boil, then reduce heat to low and simmer, whisking occasionally, for 3 minutes until slightly thickened. Remove from heat and set aside.

2. 2

   Prepare the beef: Pat the beef tenderloin pieces dry with paper towels. Season generously with salt and pepper. Heat 1 tablespoon butter with 1 tablespoon olive oil in a 12-inch heavy skillet over medium-high heat until the foam subsides. Working in two batches to avoid overcrowding, sauté the beef, turning once, until browned on both sides but still pink inside, about 1 minute per batch. Transfer cooked beef to a plate using a slotted spoon.

3. 3

   Cook the vegetables: Add the remaining 1 tablespoon butter and 1 tablespoon olive oil to the same skillet over medium-high heat and let it become hot but not smoking. Add the sliced shallots and sauté, stirring occasionally, until golden brown, about 3 minutes. Add the cremini mushrooms and continue sautéing, stirring occasionally, for 8 to 10 minutes until any liquid released by the mushrooms evaporates and they turn golden brown. Return the cooked beef and any accumulated juices to the skillet, stir to combine, then transfer everything to a serving platter.

4. 4

   Finish the sauce: Gently reheat the sauce over low heat, stirring occasionally, but do not allow it to boil. Remove from heat and whisk in the sour cream, Dijon mustard, fresh dill, and a pinch each of salt and pepper. Pour the creamy sauce over the beef and vegetables, and serve immediately over buttered egg noodles.