Cook the pasta: Bring a pot of salted water to a boil and follow the package instructions to cook the pasta until al dente. Reserve ¼–½ cup of the pasta water before draining.
Render the pancetta: Add diced pancetta to a large cold skillet. Turn the heat to medium and cook until the fat renders and the pancetta turns lightly crisp, about 5-6 minutes.
Sauté the aromatics: Add the shallot and the garlic to the pan over medium heat and saute until fragrant, about 2 minutes. Season with a pinch of salt.
Add butter and miso: Reduce the heat to low. Add the butter and let it melt, then stir in the miso paste to combine with the aromatics, 1 minute.
Add the peas: Add-in the petite peas and warm them through briefly. They should stay bright and tender.
Add milk cream: Pour in the half-and-half. Keep the heat low and gentle, stirring until the miso paste is fully dissolved. Do not let the mixture boil or the dairy may curdle.
Combine with pasta: Add the cooked pasta directly to the skillet. Toss well so the sauce coats the noodles evenly. If needed, add 2–4 tablespoons of reserved pasta water to loosen the sauce and keep it silky.
Add the parmesan: Turn off the heat. Sprinkle in the Parmesan and stir. The sauce will thicken slightly after adding the cheese.
Finish: Transfer to a serving bowl. Add freshly ground black pepper and serve warm with extra grated Parmesan on the side.
Notes
The 1:1 ratio of miso to butter gives this miso butter pasta its balanced flavor.
The amount of miso butter should scale with the pasta. If you increase the pasta quantity, increase the miso and butter proportionally.
The sauce may look thin at first. Once tossed with the pasta, the noodles release starch, which helps thicken the sauce. Avoid reducing the sauce too much in the pan or the pasta may turn dry instead of silky.
Storage: Store in a sealed container in the refrigerator. Best enjoyed within 4 days.
Reheat: This pasta is best enjoyed fresh, when the sauce is silky and glossy. If reheating, warm gently on a stovetop with a splash of milk or water to loosen the sauce.