Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Brown the beef cubes on all sides for about 5–7 minutes, then transfer to the slow cooker.

In the same skillet, add more olive oil if needed, and sauté diced onion and minced garlic over medium heat for 3–4 minutes until translucent.

Add sliced mushrooms, and cook for an additional 5 minutes until browned. Stir in 2 tablespoons of Dijon mustard and Worcestershire sauce, then pour in 2 cups of beef broth, seasoning with salt and pepper.

Bring the mixture to a simmer for 2–3 minutes before transferring it to the slow cooker with the beef and vegetables. Cover and cook on low for 6–8 hours or high for 3–4 hours.

30 minutes before serving, stir in 1 cup of heavy cream. If needed, dissolve 1 tablespoon of cornstarch in 2 tablespoons of cold water and stir it in for thicker sauce.

Garnish with fresh parsley before serving hot over mashed potatoes, rice, or buttered egg noodles.