1. Remove the coarse stems from the rosemary.
2. Mix all the ingredients for the pesto except for the salt , pepper and lemon juice into a homogeneous mixture.
3. Season to taste with salt, pepper and lemon. You now have a pesto.
4. Spread a thin layer of the pesto on the bread before adding thin slices of cheese. Close with another slice of bread.
5. Heat the oven to 150°C.
6. In a little oil, fry each sandwich on each side until golden.
7. This will only take a short time, but to make sure the cheese is completely melted, it should then have a couple of minutes in the oven.
If you are making lots of sandwiches, then reduce the oven temperature to 110-120°C. Then it will keep them hot.