Preheat oven to 190°C with racks in the middle and lower third.
Heat 2 tbsp olive oil (3 tbsp) in a Dutch oven over medium heat. Cook onion (150 g) with a pinch salt (1 tsp) until translucent, ~5 min. Add garlic (2), cook 1-2 min.
Add 960ml broth (1 1/4 l) (or 720ml broth + 240ml water), cover, bring to boil. Off heat, stir in rice (300 g). Cover and bake 55 min.
Meanwhile trim asparagus (450 g) and slice into 4cm pieces; toss on a baking sheet with 1 tbsp olive oil (3 tbsp), salt (1 tsp) and pepper.
At 55 min, put asparagus on lower rack. Stir peas (225 g) into the pot, cover, bake 10 min more.
Remove pot (leave asparagus 5-10 min more until tender). Stir in remaining 240ml broth (1 1/4 l), Parmesan (100 g), wine (120 ml), butter (45 g), salt (1 tsp), pepper, red pepper flakes and lemon zest and juice (1/2).
Stir vigorously 2-3 min until creamy. Fold in roasted asparagus (450 g), season, serve topped with parsley.