Keep the broth at a very slow, steady simmer near the risotto pot.
In a broad, sturdy pot over medium heat, bring the meat sauce to a steady, gentle simmer. Add rice and stir about 1 minute until the grains are coated.
Add 1/2 cup (120 ml) simmering broth and continue cooking as for basic risotto, adding broth as needed.
Finish cooking with broth, or with water if the broth runs out. Cook until rice is tender but firm, with no liquid remaining in the pot.
Off heat, stir in butter and all the Parmesan until melted and clinging. Taste and correct for salt. Serve promptly with extra cheese.