Method
Prep:10min  ›  Cook:10min  ›  Ready in:20min 

1. Using a fork, whisk the eggs with 1 tbsp cold water and freshly ground black pepper in a bowl until frothy.
2. Heat the butter in an 18cm omelette pan or non-stick frying pan over a moderate heat until foaming. Tilt the pan to coat the bottom with the butter, then pour in the beaten egg mixture. Cook for about 1 minute, stirring gently with a spatula and pulling the cooked egg in from the edges so that the unset egg runs onto the hot pan and starts cooking.
3. When the egg is lightly set, stop stirring and scatter over the chopped tomatoes. Cook for a further 30 seconds or until the egg is just set and golden underneath. Remove from the heat.
4. Sprinkle over the cheese and watercress, then slide the omelette onto a warmed plate, folding it over in half as it slides from the pan. Serve immediately.

cook's tip

Plum tomatoes are a good variety to use here as they are firm-fleshed and less watery than regular tomatoes. For strict vegetarians, use the Cheddar cheese option.