Eviscerate the tench, fillet and remove skin. Prepare the fish broth by browning the washed and diced vegetables, then add the backbone, head and skin of fish and brown for a few minutes. Add half a glass white wine, leave to evaporate, then add 1 lt cold water and reduce to half. Remove the bones from the fillet of tench and cut into cubes. Brown a quarter of chopped onion in a pan with a drizzle of oil and add the tench continuing on high flame for a few minutes; add salt and pepper to taste, then add a glass of white wine, the tomato purée and cook on a low heat for about half an hour, adding if necessary some fish broth. Peel and wash the asparagus, cut into rounds and fry with a drizzle of oil and onion, Add salt and pepper to taste and continue cooking for 15 minutes. Boil the sieved fish broth in a pan, add the rice and after 4 minutes add the asparagus and continue to cook for a quarter of an hour on a low heat and if necessary add vegetable broth. Remove from heat when cooked and stir in the grated cheese and a knob of butter. Place the rice in a dish and in the centre add the tench sauce. Garnish with asparagus tips.