Beef Wellington

Method

1. Pat the 180 g fillet steak dry and season it generously with salt and black pepper. Heat a heavy frying pan over the highest heat with 1 tsp of vegetable oil until it just smokes, then sear the beef for 1 minute on each side and 1 minute on each end, so every surface is browned but the inside is raw. Lift onto a plate, brush all over with 1 tsp of Dijon mustard while still hot, and chill uncovered for 20 minutes.
2. Chop 100 g of chestnut mushrooms as finely as you can, almost to a paste. Wipe out the pan, set it over medium heat with 1 tsp of butter and soften 1 finely chopped shallot for 2 minutes, then add the mushrooms and the leaves from 1 sprig of thyme. Cook 10-12 minutes, stirring often, until the mushrooms have given up all their water and the mixture holds together in a dry, dark clump.
3. Pour in 1 tbsp of Madeira and stir until it has completely evaporated, about 1 minute. Season the duxelles lightly, spread it on a cold plate and leave until completely cool — any warmth or moisture will make the pastry sodden.