1Place the beef cutlet between two layers of plastic wrap or in a plastic bag and pound them as this as you can without braking or punching holes into them, set aside.
2Bring a pot of salted water to a boil.
3Wash the spinach thoroughly and cook them in the boiling water for a couple of minutes, then drain and rinse under cold water. Squeeze them dry and chop fine, set aside.
4In a bowl mix together eggs, milk and Parmesan, lightly season with salt and freshly ground pepper; whip until evenly mixed. Add the chopped spinach and mix well.
5Melt a small tab of butter in an 8-inch non-stick pan; pour 1/3 of the egg batter, cover with a lid and cook over a medium low flame for about 5-7 minutes. The frittata will be ready when the edges start browning lightly and the top of the eggs is firm and not runny. Slide off the frittata from the pan using a rubber spatula and set aside to cool, repeat this process to yield 3 small frittate.
6On a large cutting board place a beef cutlet and position a frittata on top of it; roll it and secure it with the twine, making sure though not to tighten the twine too much as it can break through the meat or push the frittata out of the roll.
7In a large pan over medium-high heat sauté the chopped garlic and the sprig of Rosemary in 2 tablespoons of Olive oil for about 4-5 minutes, then add the beef rolls.
8Sear the meat evenly rolling it into the pan without lowering the flame, then add the wine and let the alcohol evaporate. Lower the flame to a low medium and cook partially covered with a lid for about 25-30 minutes.
9When ready place the rolls on a cutting board and allow a few minutes for the meat to cool off a bit, then slice thin and serve dressed with the cooking sauce.