HEAT oven to 375°F.
BRUSH bottom and side of crust lightly with egg white; discard remaining egg white. Bake 5 min.; set aside. Reduce oven temperature to 350°F. Beat margarine and sugar in medium bowl with mixer until well blended. Add next 4 ingredients; mix well. Stir in nuts. Spread onto bottom of crust.
BAKE 30 to 35 min. or until filling is lightly browned and set in center. Cool completely. Meanwhile, cook half-and-half and chocolate in saucepan on low heat until chocolate is completely melted and mixture is well blended, stirring constantly. Remove from heat; cool 30 min. or until thickened.
SPREAD chocolate mixture over pie. Refrigerate until firm.