Preheat the oven to 180ºC/350ºF/Gas 4, and preheat grill. Brush four ovenproof ramekins with softened butter, add three slices of tomato into each bowl, overlapping slightly.
Sprinkle half the grated cheese evenly over tomatoes. Crack two eggs into each and season with salt and pepper.
Put ramekins into a deep oven tray and half fill it with hot water (creating a Bain Marie). Transfer to oven and bake for 12 mins the yolks are almost set but slightly runny. Remove from cheese and grill until golden.
Sprinkle with chives and serve immediately.