Cook pasta in salted water, reserving about 1/2 a cup.
Add butter to a pan and once it’s melted, add asparagus and walnuts. Season with salt and pepper. Cook until softened and browned.
Once pasta is cooked, strain and return to pot or saucepan and turn heat to low. Add scoops of mascarpone, and stir until it’s melted into the pasta. Slowly add in pasta water a little at a time and allow sauce to thicken. Add in asparagus and walnuts, stirring until combined.
Add in lemon juice slowly and taste until you feel like you have enough. You can really play around with your amounts of lemon, mascarpone, water to get the right creamy consistency and level of acid from the lemons. Season everything with salt and pepper and serve with grated parm overtop. Enjoy!