In a large skillet, melt butter with olive oil over medium-high heat.
Vegetables & Seasoning
Add mushrooms and sauté undisturbed until golden, about 5–6 minutes.
Stir in onion and cook until translucent, about 3 minutes.
Add garlic and cook until fragrant, about 30 seconds.
Mix in tomato paste, smoked paprika, and red pepper flakes; cook for 1 minute.
Thickening & Finish
Sprinkle flour over vegetables, stirring and cooking for 2 minutes.
Whisk in beef broth, bring to a simmer, and cook until slightly thickened, about 5 minutes.
Remove from heat and stir in sour cream until smooth. Season with salt and pepper.
Notes
When prepping, I pat mushrooms thoroughly dry and let them sit at room temperature for 10 minutes to enhance browning.Pat mushrooms dry before cooking to avoid excess moisture; letting them sear undisturbed developed a deep, nutty aroma.I froze single-serve jars with parchment-paper liners and found the texture stayed smooth after reheating on low heat.