Peel the potatoes and cut them into round slices. Arrange them in an oven dish along with the finely chopped ham. Pour oil and a little water over them. Put foil on and bake at 392°F (200 °C) about 40 min.
In the meantime, beat the powder for the Carbonara sauce with the milk. Once you remove the foil from the oven dish, pour the sauce over the potatoes.
Return to the oven for 5 min., then take it out and sprinkle with grated cheese.
Return to the oven again until the cheese crisps.