Using a small pan, cover the eggs with cold water. Bring up to a boil then switch off the heat. Cover and leave for exactly 5 minutes, then put the pan under a cold running tap for a couple of minutes; the yolks will be soft in the centre done this way.
Carefully peel the eggs [under a running tap helps here]. I use a mini mouli legume to mash the eggs, but a fork works almost as well. Mix with the remaining deviled egg ingredients and stir well.
Spread onto the buttered toast and lay 2 slices of cods roe upon each. Grind over some black pepper and serve with lemon and watercress.