Crack those eggs into a bowl. Pour in the milk. Season it with salt and pepper. Whisk away until smooth.
Heat up a non-stick pan. Add that butter and let it melt, ensuring it covers the pan’s base.
Pour your egg mixture into the pan. Let it cook for 2 minutes without stirring. You want it slightly set.
Now, spread the spinach, tomatoes, and cheese on one half of the slightly set egg.
Once the edges are golden, which might take around 4-5 minutes, fold the omelette in half. Let it sit for another 2 minutes to allow the cheese to melt.
Transfer to a plate, sprinkle with chives, and serve hot.