For the yorkshire puddings, mix the egg into the flour then slowly add the water and milk to the mix, whisking everything together constantly to avoid lumps. Add the thyme leaves and season with salt and pepper. .
Put a few drops of oil into each hole of a mini muffin tin and put into the oven to heat. When the tray is hot, pour the mixture into each hole, filling to about ⅔ rds full and place back in the oven. Cook for about 10 - 12 minutes until the yorkshire puddings have puffed up. Remove from the oven and cool on a cooling rack.
To make the horseradish cream, mix the creme fraiche, horseradish sauce and some salt and pepper together in a small bowl and place into a piping bag.
Place a frying pan over a medium-high heat and allow to warm up. Rub the beef with the beef dripping and season well on all sides with salt and pepper. Place into the hot pan and cook for about 2 minutes each side. Turn the heat down and add the butter and garlic cloves and baste the fillets with the butter as it melts. When done to your liking, remove from the pan and place on a warmed plate, pour over the pan juices and rest for 5 - 6 minutes. When fully rested, slice thinly.
To assemble, arrange the beef slices on the mini Yorkshire puddings. Snip the end off the piping bag containing the horseradish cream and pipe a good amount onto each yorkshire pudding. Garnish with a few watercress leaves and finally grate over a little fresh horseradish.