1. Heat oven to 375 degrees F. Coat shallow 2-1/2-quart oval casserole with cooking spray. Cook linguini following package directions (if making ahead-see Tip below-cook pasta just until barely tender). Drain linguini; rinse with cold water; drain. Return to pot.
2. In large skillet, melt 2 tablespoons butter over medium-high. Add chicken; saute 3 minutes, just until cooked through. With slotted spoon, remove chicken to a bowl.
3. In same skillet, melt remaining 2 tablespoons butter. Add onion; saute 3 minutes. Remove from heat. Stir in flour, salt, nutmeg and cayenne. Gradually stir in 2 cups half-and-half. Boil, stirring, until slightly thickened, 2 minutes. Remove from heat.
4. In small bowl, combine yolks, remaining half-and-half and sherry. Stir into skillet along with 1/2 cup cheese and tarragon. Remove 1 cup sauce and add to linguini. Spoon linguini into prepared casserole, arranging around edge (or, if making ahead, spread over bottom of casserole).
5. Into remaining sauce in skillet, stir chicken, artichokes and peas. Spoon into center of casserole inside linguini (or over linguini if making ahead). Sprinkle with remaining 1/2 cup cheese; cover with nonstick foil or regular foil coated with cooking spray.
6. Bake in 375 degrees F oven 45 minutes. Uncover; bake 5 minutes. Let stand 10 minutes.