Step 1: Season and Sear the Beef
In a medium bowl, toss the thinly sliced steak strips with the Worcestershire sauce, smoked paprika, salt, and black pepper. Heat 1 tablespoon of olive oil in a large, heavy-bottomed skillet or Dutch oven over medium-high heat. Once shimmering, add the beef in a single layer, working in batches if necessary to avoid overcrowding. Sear for about 1-2 minutes per side, just until browned. The beef does not need to be cooked through at this stage. Remove the beef with a slotted spoon and set it aside on a plate.

Step 2: Sauté the Mushrooms and Aromatics
Add the remaining 1 tablespoon of olive oil to the same skillet. Add the sliced mushrooms and onions. Cook, stirring occasionally, for 6-8 minutes, until the mushrooms have released their liquid and are deeply browned, and the onions are soft and translucent. In the last minute, add the minced garlic and cook until fragrant.

Step 3: Create the Flavorful Roux
Push the mushroom and onion mixture to the sides of the skillet. Reduce the heat to medium. Add the 3 tablespoons of butter to the center of the skillet. Once melted, sprinkle the 3 tablespoons of flour over the butter. Whisk continuously to form a paste (a roux) and cook for 1-2 minutes until it turns a light golden brown and smells nutty.

Step 4: Deglaze and Build the Sauce
Gradually pour in the beef broth while whisking constantly to incorporate the roux smoothly and prevent any lumps from forming. Scrape up any browned bits from the bottom of the pan—this is packed with flavor. Whisk in the Dijon mustard, tomato paste, and dried thyme until fully dissolved.

Step 5: Simmer and Cook the Tortellini
Bring the sauce to a gentle simmer. Add the entire package of fresh cheese tortellini directly into the skillet, submerging them in the liquid. Reduce the heat to medium-low, cover the skillet, and let it simmer for the time indicated on the tortellini package, usually about 7-9 minutes, stirring occasionally. The sauce will thicken as the tortellini cooks.

Step 6: Reintroduce the Beef and Finish with Cream
Once the tortellini is tender, return the seared beef and any accumulated juices to the skillet. Stir to combine and heat the beef through for about 1-2 minutes. Remove the skillet from the heat entirely. This is crucial for the next step.

Step 7: Temper and Incorporate the Sour Cream
In a small bowl, ladle a small amount of the hot sauce into the room-temperature sour cream and heavy cream. Whisk vigorously. This “tempers” the dairy, preventing it from curdling. Slowly pour this tempered mixture back into the skillet, stirring constantly until the sauce is uniformly creamy and luxurious.