Whisk the eggs and milk together for the pancakes. Slowly whisk in some sieved flour until you have a batter consistency.
Just before you make the pancakes, add the chopped herbs and some seasoning to the butter. Make three pancakes and fry. Allow to cool.
Seal the beef fillet in a hot pan with a little oil. Allow to cool then brush with a mix of the raw egg white and English mustard.
Wrap the beef in the herb pancakes (one layer thick all round).
Roll out a piece of puff pastry big enough to generously wrap the beef. Brush with the egg wash and seal the pastry around the beef.
Brush the top with egg wash before baking.
Bake on silicon paper for about 12 minutes at 180C/350F/Gas 4 and allow to rest for 5 minutes.
Blanch the spinach in hot water and refresh in cold water. Reduce the double cream over a low heat and add the spinach.
When the mixture is thick and rich, remove from the heat and allow to rest.
Slice the beef and top with the spinach. Serve.