Set a pot of water to boil. Drop in pasta and cook until al dente, about 8-10 minutes.
While you're waiting for the water and pasta, heat a large saute pan and melt butter. Add flour and stir until beginning to slightly brown. You want to cook out the "flour-y" taste and get it somewhat nutty.
Add cream and stir until starting to boil and slightly thicken.
Turn the heat down just a tad, and add in lemon juice and parmesan cheese. Season with salt and pepper to taste.
In a microwave safe bowl, cook the peas for about 1-2 minutes. Just to warm them through. Then add to pan with sauce, along with ham.
Drain the pasta and add to cream sauce. Mix until everything is well-combined and serve hot! Top with fresh parmesan cheese, if desired!