Preheat the oven to 400 degrees . In a small saucepan, melt the butter over medium heat. Whisk in the flour until smooth. Slowly whisk in the heavy cream and cook, stirring continuously, until thickened, about 5 minutes. Set the cream sauce aside; then stir in the salt.
In a medium bowl, combine the ricotta and mozzarella and the egg.
Spread a thin layer of the cream sauce (about 1 1/2 cups) in the bottom of a 9-by-9-inch baking dish. Arrange an egg-roll wrapper on a work surface. Spread 3 tablespoons of the ricotta mixture over the wrapper, cover with a slice of ham, then roll up to form a log, jelly-roll style. Repeat with the remaining wrappers and place the cannelloni, seam side down, in a single layer in the baking dish.
Spoon the remaining cream sauce over the cannelloni, top with the Parmigiano-Reggiano and bake for 20 minutes, or until golden brown and bubbly.