Start with a great batch of "Homemade Beef Stock".  Melt the butter in a very large skillet over high heat.  Add the sirloin and stir until the meat browns.  Add the mushrooms and stir until the mushrooms are just soft.  Add salt and pepper and stir.  Reduce to medium heat and remove the meat and mushrooms to a bowl using a slotted spoon, leaving the liquid in the skillet.  Whisk flour into the boiling liquid in the skillet.  Continue whisking and adding flour until the mixture becomes very thick.  Add the paprika and continue whisking.  Gradually add the beef stock, stirring as you go.  Gradually add the sour cream, stirring until the mixture is well blended.  Return the meat and mushrooms to the skillet.  Reduce to low heat and simmer for 30 minutes.  Serve over brown rice.

Our comments:  This is one our staples.  Cook large batches so you can freeze the leftovers in small containers.  It makes a great fast meal.