Fillet of Beef in Creamy Grape-Mustard Sauce with Paté

Here's a fantastic meal my uncle prepared about three weeks ago. This really struck a note with me, so I thought I'd record it here.

Ingredients:
A small onion - chopped, about half a dozen button mushrooms - quartered, one fillet of beef - sliced very thinly, some flour for coating, lots of butter, 250ml of cream, a cup of grapes - halved, one tablespoon of ground mustard seeds, 150g of cranberry paté.
Preparation:

• Melt butter in a pan, fry chopped onions and mushrooms. Meanwhile, melt more butter separately to coat fillet slices. Turn slices in butter, then flour. Add to pan when onions are glassy, brown on both sides.
• Turn heat to low. Puree the halved grapes, strain, add grape juice with mustard seeds to pan.
• Add cream, let simmer for about 5 minutes.
• Add paté, mix in well with a spoon or fork. Let everything simmer for another 5 minutes.
  
• Season, serve over butter spätzle.

As in all good cooking, I find the properties of this meal are not the sum of its parts.