Season the chicken breasts on both sides with salt and black pepper, then sear them in olive oil in a skillet over medium heat.

Continue turning the chicken until browned on both sides. Remove and place them in a baking dish, pouring any excess olive oil from the pan into the dish.

Finely chop the rosemary. If you don't have fresh rosemary, use dried, but reduce the amount.

In a small bowl, mix together all the sauce ingredients: melted butter, lemon juice, chicken broth, garlic, and rosemary. Add a pinch of salt and black pepper.

Pour the sauce over the chicken breasts, cover with aluminum foil, and bake in a preheated oven at 350°F (180°C) for about 25 minutes. Near the end, remove the foil and let the chicken brown on top.

Meanwhile, start making the mashed potatoes. Cut the potatoes into cubes and boil them in salted water until very tender. Drain and return them to the pot.

Mash the potatoes well with a potato masher until completely smooth.

Heat the milk and add it to the potatoes, stirring well until the potatoes absorb the milk.

Return the pot to the heat, add the butter, salt, and nutmeg, and stir until well combined. Remove from heat.

Once the chicken is browned, take it out of the oven. Serve a portion of mashed potatoes on a plate, top with a chicken breast, and spoon some of the sauce over the potatoes.

Serve the rosemary chicken breasts with mashed potatoes hot or warm for an easy, nutritious, and very tasty dinner.