Prepare the spinach, remove it from the heat and cover the pan to keep it warm.
Season the scallopine lightly with salt and pepper, keeping in mind that the prosciutto is cured with salt. Cover each scallopine with a half slice of the prosciutto. Tap the prosciutto with the back of a knife so it adheres well to the meat. Center a sage leaf over the prosciutto and fasten it in place with a tooth pick, weaving the toothpick in and out as if you were taking a stitch. (Alternatively, you can place the sage leaf directly over the scallopine and cover it with the prosciutto.)

Dredge the scallopine in the flour to lightly coat both sides. Tap off excess flour. Heat 3 tablespoons olive oil and 2 tablespoons of the butter in a large, heavy skillet over medium heat until the butter is foaming. Slip as many of the scallopine, prosciutto side down, into the pan as fit without touching. Cook just until the prosciutto is light golden, about 2 minutes. (Overcooking will toughen the prosciutto.) Turn and cook until the second side is browned, about 2 minutes. Remove and drain on paper towels. Repeat with remaining scallopine, adding more oil if necessary.

Remove all the scallopine from the skillet and pour off the oil. Return the pan to the heat and pour in the wine. Add the remaining 4 tablespoons butter and cook until the wine is reduced by about half, about 3 minutes. Pour in the chicken stock and bring to a vigorous boil. Tuck the scallopine into the sauce. Simmer until the sauce is reduced and lightly thickened, about 3 to 4 minutes. Taste and season with salt and pepper, if necessary.

To serve, spoon the spinach in a mound in the center of each plate. Arrange the saltimbocca over the spinach. Spoon some of the pan sauce over the scallopine and serve immediately.