Beef Wellington is a favourite celebration dish. If it's made well, it's bound to impress, but it's not easy to get the beef fillet cooked right while maintaining a firm and crisp pastry shell. Plus the fillet of beef is frighteningly expensive. As an experiment, I decided to try making beef wellington with a cheaper cut of beef (I ended up with topside, which cost less than half the price of beef fillet), and pre-cooking it using the sous vide technique. It turned out really well. Some versions of beef wellington have the meat wrapped in Parma ham, and some include a layer of pâté de foie gras. I think the dish is plenty rich enough just with the meat coated in mushroom duxelles, so that's what I'm doing, along with crêpes to stop the bottom going soggy.
Eggwash - a beaten egg with a splash of milk.