Bring a large pot of lightly salted water to boil over high heat. Prepare pasta following package directions, stirring frequently. Drain.

Meanwhile, mix 1/4 cup of the half-and-half with the cornstarch; stir well and set aside. In a medium-size saucepan, add the remaining 1-3/4 cups half-and-half and place over medium-high heat. Stir in 1/2 teaspoon of the garlic salt and the nutmeg. Bring to a simmer and stir in the cornstarch mixture; cook for 30 seconds or until slightly thickened.

Take sauce off heat and whisk in the cheese and the mustard until smooth. Stir in the peas. Keep warm.

Heat olive oil in a large skillet over medium-high heat. Add shrimp and remaining 1/4 teaspoon garlic salt; cook for 3 minutes per side until cooked through. Stir cream sauce into skillet with shrimp; add pasta and toss to coat. Serve immediately with additional cheese. Garnish with basil, if desired.