For the vegetables:
For the polenta:
For the ricotta filling:
For the dish:
8 ounces Parmigiana-Reggiano, grated
For the vegetables, prepare a grill, grill each type of vegetable, season and set aside to cool.
For the polenta, in a large saucepan, bring the milk, stock, salt and pepper to a boil. Remove pan from the heat and whisk in the polenta, one handful at a time. Return the mixture to low-medium heat, stirring often until thick and creamy. Fold in the butter and Parmigiana-Reggiano, season, and set aside to keep warm.
For the ricotta filling, in a bowl, stir milk into the ricotta with a wooden spoon until it is softened and smooth. Incorporate the tomato powder and season.
To assemble, preheat oven to 400° and butter a large 2" deep, oven-proof casserole dish. Pour in ½ the polenta, setting the remainder aside to keep warm, and allow to set until slightly firm. Smooth _ of the tomato ricotta over it, align a row of asparagus on top, and spread another _ of the ricotta over the spears to cover. Arrange the vegetables in individual layers, spread with the last _ ricotta, place a row of the remaining asparagus on top, and spread with the rest of the polenta. Cover the surface with grated cheese and set for 10 minutes. Bake at 350° for 1½ hours.