Wash and dry all produce. Bring a large pot of salted water to a boil. Trim, then thinly slice scallions, keeping greens and whites separate. Zest 1 tsp zest from lemon, then cut into wedges. Separate egg yolks from whites. Place yolks in a large bowl (discard whites or save for another use).

Heat a medium pan over medium-high heat. Add pancetta and cook, stirring occasionally, until nearly crisp, 3-5 minutes. Add scallion whites and cook, tossing, until softened and pancetta is fully crisp, 1-2 minutes more. Remove from pan with a slotted spoon; set aside on a paper-towel-lined plate.

Once water is boiling, add penne to pot. Cook, stirring occasionally, until just shy of al dente, about 8 minutes, then add peas. Continue cooking until peas are warmed through and pasta is al dente, about 2 minutes more. Scoop out and reserve 1/2 cup pasta cooking water, then drain.

While pasta boils, add sour cream and half the Parmesan to bowl with egg yolks. Whisk or beat vigorously with a fork until well-combined. As soon as you’ve scooped out pasta cooking water, add 3 TBSP of it to egg yolk mixture and whisk vigorously to combine and heat through.

Add drained penne and peas to bowl with sauce immediately after draining, followed by pancetta, half the scallion greens, and 1 TBSP butter. Toss to combine and thoroughly coat. (TIP: If mixture seems dry, add more pasta cooking water—start with 2 TBSP and go up from there.) Season generously with salt, pepper, and a squeeze or two of lemon juice.

Divide penne mixture between plates. Sprinkle with remaining Parmesan and scallion greens. Sprinkle with lemon zest and serve with any remaining lemon wedges on the side for squeezing over.