With a meat mallet, beat the chicken breasts between two sheets of clingfilm on a board until the breasts are 1/2in thin. Lightly dust the breasts with flour.
Heat 2 tablespoons of the olive oil in a medium frying pan and fry the chicken for about 1 minute on each side. Add the Marsala and flame for about 15 seconds, allowing the alcohol to evaporate.
Add the cream and the dill, season with salt and pepper and cook, uncovered, over a low heat for about 4 minutes to allow the sauce to thicken.
Meanwhile, slice the potatoes about 1/2in thick. Heat the remaining oil in a second frying pan, fry the garlic and rosemary for 1 minute, then add the potatoes. Season with salt and pepper and cook over a medium heat for 5 minutes or until golden on both sides.
Place a chicken breast on each plate and surround with sautéed potatoes. Drizzle some of the sauce over the chicken and serve immediately.