Foryoueats: Ham Tortellini Alfredo

2 packages (9 ounces each) refrigerated cheese tortellini

1/2 cup chopped onion

1/3 cup butter, cubed

1-1/2 cups frozen peas, thawed

1 cup thinly sliced fresh mushrooms

1 cup cubed fully cooked ham

1-3/4 cups heavy whipping cream

1/4 teaspoon coarsely ground pepper

3/4 cup grated Parmesan cheese

Shredded Parmesan cheese, optional

Ham Tortellini Alfredo