Lemon Dijon Pasta & Peas

Cleaning out the cookbooks and found this recipe that I haven't made in a while.

5 ounces (2 cups) uncooked dried radiatore (pasta nuggets)
2 cups frozen peas
1 tablespoon butter
1 tablespoon all-purpose flour
1/4 teaspoon salt
1/8 teaspoon white pepper
1 cup milk
2 tablespoons Dijon-style mustard
1 tablespoon chopped onion
2 teaspoons lemon juice

Cook pasta according to package directions, adding peas during last 5 minutes of cooking. Rinse with hot water; drain.

Meanwhile, in 3-quart saucepan melt butter until sizzling; stir in flour, salt and pepper until smooth and bubbly (1 minute).

Gradually stir in milk and mustard. Cook over medium heat, stirring constantly, until mixture comes to a full boil (4 to 6 minutes); boil 1 minute.

Remove from heat; stir in onion and lemon juice. Immediately add pasta mixture; toss to coat with sauce.