Place the gnocchi in a lightly greased (9″ x 12″) baking pan. Set aside.
In a medium sauce pan over medium heat, whisk together the broth, cream and flour. Continue whisking until the mixture starts to thicken, about 6 minutes. If you don’t see the sauce starting to thicken, check that the flour is not on the sides of the pan, it likes to hide down there. Add the pepper and stir. Add the spinach and prosciutto to the thickened cream and toss to coat all the leaves and slices. Pour the cream, spinach and prosciutto over the gnocchi and spread out to cover the pasta evenly.
Top with spoonfuls of ricotta and sprinkle with Parmigiano-Reggiano. Bake until the top is golden brown, about 35 minutes.