Melt 2 tablespoon butter in a 3-quart saucepan over medium heat. Cook and stir onion until softened and turning translucent, about 1 minute. Add garlic and cook for another minute. Stir in the rice, asparagus, and stock. Cover and reduce heat to medium-low.

Stir occasionally to prevent the rice from sticking to the bottom of the pan. Continue cooking until the rice is tender, about 10 minutes.

Turn off the heat and gently stir in the Parmesan cheese and remaining butter. Serve immediately.