In a large skillet over medium, heat olive oil and swirl the pan to coat with oil evenly. Add the seasoned chicken cutlets, and cook for about 3 minutes per side or until the internal temperature is 165°F/74°C. Remove onto a plate and set aside.
Add 1 tablespoon of butter to the pan along with the garlic, saute for 1 minute.
Then add the chicken stock. Deglaze and scrape the bottom of the pan with a spatula to get anything stuck to the pan (lots of flavor there).
Add rosemary sprigs to the stock, and allow it to reduce over medium heat (takes about 7-8 minutes). Add to the pan the juices that come out of the chicken as it rests.
Add 2 tablespoons of cold butter and stir it in so it’s emulsified with the sauce (it will help the sauce thicken).
The sauce is ready when it coats the back of your spoon, and when you run your finger through it, you get a sharp line. Remove from heat, add lemon juice, season with salt and pepper to taste. And stir to combine.
If serving immediately, add the chicken to the pan/sauce.