Season meat with salt & pepper.  Heat large non-stick skillet or dutch oven over high heat and sear meat on all sides, for about a minute (total).  Work is small batches so meat does not give off liquid.  Remove the meat to a plate and cover.  Reduce heat to medium or medium high and add butter to the pan.  When butter begins to melt, add garlic for 1 minute, then add onions and mushrooms.  Saute until deep golden, about 20 minutes.  While this is cooking, blend broth, mustard, heavy cream and sour cream together in a bowl.  After mushrooms/onions are browned, lower heat on this mixture, add flour and cook stirring for a minute so all the flour is mixed in and not clumpy.  Whisk in liquids, any meat juices that have accumulated on the plate and simmer without boiling until sauce thickens, about 5 minutes.  Return meat to sauce, add peas and heat, without boiling until meat is warmed through.  Season to taste with salt & pepper (note: I did not add any salt, only pepper).  Stir in parsley and serve over noodles.