Put a pot filled with water on the hob, to boil. Once the water is bubbling add in the pasta and stir until cooked.
Whilst the water is boiling, add 2 mushrooms, quartered, into a blender. Melt the butter to liquid in a bowl, and add that in the blender too, with the flour and milk. Blend the ingredients to a mush.
Put the mush in a pot on the hob and melt until liquid, best on Gas Mark 3. Add seasonings, salt, pepper and a bit of mustard. Meanwhile, add the rest of the mushrooms, (halved) and a bit of butter into a saucepan and fry the mushrooms.