Fill a large pot with water and set it over high heat to bring it to a boil.

While the water heats, finely chop the onion, dice the ham, cut the cream cheese into small pieces, and grate the Parmesan if needed.

Set a large skillet on the stove over medium heat so it is ready when the pasta cooks.

When the water reaches a full boil, add 1 tablespoon kosher salt and the shell pasta to the pot. Stir well so the pasta does not stick together.

Cook the pasta according to the package directions until it is tender with a little firmness in the center, usually 9 to 11 minutes. Stir once or twice as it cooks.

Add the olive oil to the warm skillet.

Add the chopped onion to the skillet. Cook for 4 to 5 minutes, stirring now and then, until the onion is soft and lightly golden at the edges.

Add the diced ham to the skillet. Cook for 2 to 3 minutes, stirring a few times, until the ham is heated through and lightly browned in spots.

Add the frozen peas to the skillet. Cook for 1 to 2 minutes, stirring, until the peas are hot and bright green.

When the pasta is almost done, scoop 1 1/2 cups of the pasta cooking water out of the pot and set it aside in a heatproof measuring cup.

Add the cream cheese pieces to the skillet with 3/4 cup of the reserved pasta water. Stir until the cream cheese melts and the liquid looks smooth.

Add 3/4 cup of the grated Parmesan and the black pepper to the skillet. Stir until the cheese melts into a loose sauce. If the sauce looks thick, add a small splash of the reserved pasta water.