Slice mushrooms thin. Divide into two piles: ⅔ for cooking down, ⅓ for adding at the end.
Sauté aromatics. Melt butter with olive oil in skillet over medium heat. Add onion; cook 2 min. Add garlic; cook 30 seconds.
Brown the mushrooms. Add the larger ⅔ pile. Cook 5–6 min, stirring, until water cooks off and edges are deeply browned.
Toast the flour. Sprinkle 1 tsp flour over mushrooms; stir constantly 45 seconds.
Build the sauce. Slowly pour in beef broth while stirring. Add cream of mushroom soup, Worcestershire, soy sauce, onion powder, garlic powder, and black pepper. Whisk smooth.
Simmer. Reduce heat to medium-low. Simmer 6–8 min, stirring occasionally, until sauce coats the back of a spoon (thinner than gravy).
Add second mushrooms. Stir in remaining ⅓ of sliced mushrooms. Cook 2 min until just softened.
Taste. Adjust salt and pepper. Serve immediately or store.