Salted egg yolk prawns are a Cantonese restaurant showpiece, and the trick is entirely in the sauce. Cooked salted duck egg yolks are mashed and fried in butter until they foam into a sandy golden coating that sticks to everything it touches.
Buy the yolks ready-cooked from an Asian grocer if you can, or steam the whole salted eggs and scoop them out. Mash them properly: any lump that survives the fork will still be a lump on the plate.