Mix the sour cream and crème fraîche with the broth and pour this mixture into a large baking dish. Make several incisions into the well washed potatoes, but do not cut them all the way through, they should still be connected at the bottom. The distances between the cuts should be similar to that of an egg slicer. Place the potatoes in the pan with the cut side up, but only side by side, not stacked on top of each other, so that they are about halfway in the sauce. Bake at 200 ° C for approx. 45 - 60 minutes, until the potatoes are almost cooked. In the meantime, melt the butter, add the ham and rosemary and mix in the toasted bread cubes. Spread this mixture on the potatoes and bake again until the bread cubes are nice and brown and the potatoes are cooked. Serve with the lettuce.