Start heating your oven to 180 C / 350 F / Gas Mark 4
Beat the eggs with the milk and a bit of salt and pepper. Add the tomatoes, the rosemary, the cheese, and stir.
Place a cast-iron frying pan or a frying pan with a metal handle over medium heat on the stove, and heat the butter and the olive oil in it.
Pour the egg mixture in, cook just until the edges start to set. [Optional: sprinkle a bit more cheese on top.] Put in the oven for about 10 minutes or until all set.
Invert onto a plate, and serve either warm or cold. Slice as you would a pie to serve.
Notes
Instead of 1 teaspoon dried rosemary, you can use 1 tablespoon chopped fresh rosemary. Feel free to use more if you wish, to taste. Or swap in whatever herbs you have to hand.