Heat the olive oil in a large pot or deep skillet over medium-high heat until shimmering. Add the diced onion and cook for 3-4 minutes, stirring occasionally, until it begins to soften and turn translucent. Add the ground beef, breaking it up with a spoon as it cooks, and season it with garlic powder, paprika, salt, and black pepper. Continue cooking for 5-7 minutes until the beef is fully browned and no longer pink, stirring frequently to ensure even browning. This initial browning develops deep flavor through the Maillard reaction—don't rush it or skip the browning step, as it's the foundation of the entire dish.

Stir the Dijon mustard into the browned beef mixture, coating everything evenly—the mustard adds tangy complexity and helps brighten the heavy cream that comes later. Pour in the cream of mushroom soup and stir well to combine, scraping up any browned bits from the bottom of the pot. Let this mixture bubble for about 1 minute to allow the flavors to meld slightly before adding liquid.

Add the sliced mushrooms and stir them into the sauce. Pour in the beef broth and bring the mixture to a rolling boil over medium-high heat, stirring occasionally. Once boiling, add the uncooked pasta (wide egg noodles work best here as they hold sauce beautifully) and stir to break up any clumps and prevent sticking to the bottom.

Reduce the heat to medium and let the mixture simmer for about 12 minutes, stirring occasionally, until the pasta is tender and most of the broth has been absorbed—you want it creamy, not soupy. I always taste a noodle at around the 10-minute mark to check tenderness, since pasta brands vary slightly. The dish should look thick and cohesive at this point, with minimal free liquid remaining.

Remove the pot from heat and immediately stir in the full-fat sour cream and minced garlic until fully combined and creamy. The heat from the pasta will gently warm the sour cream without curdling it—removing from heat first is essential. Fold in the fresh chopped parsley and taste the dish, adjusting salt and pepper if needed. I always add the sour cream off heat because it prevents any risk of it breaking or becoming grainy from direct heat.