Place the onion into the Thermomix bowl with butter and EVOO and chop 2 sec/speed 6. Scrape down sides of bowl and saute 5 min/Varoma/speed 1.
Meanwhile, dice the beef into quite large pieces and dust in a little bit of flour. Set aside.
Add the brandy and cook 2 min/Varoma/speed 1/MC off.
Add beef, seasoning, stock, worcestershire sauce, bay leaf, mustard to the Thermomix bowl.
Cook 8 min/Varoma/Reverse/speed soft or until tender. If you use a cheap cut you will need much longer. We recommend a Scotch fillet for this recipe.
Add the sliced mushrooms and push them down underneath the hot liquid. Cook further 2 min/Varoma/Reverse/speed soft.
When ready to serve, add the sour cream and diced pickles and stir through to combine. Serve over the mash (or puree).