Wash the basil and dry it well. Grind it "finely" with garlic. Add salt and gradually add the grated parmesan. Then add the butter and stir until you get a compact mixture. Boil the water and milk, pour the flour and stir, boil it for 15 minutes. Finally stir in the butter, parmesan and a third of the sauce. Serve the polenta with the rest of the sauce.
For the sauce: