BRING 1 1/3 cups water to a boil in a 3-quart saucepan over medium-high heat. Stir in piecrust mix, beating vigorously with a wooden spoon 1 minute or until mixture leaves sides of pan.
PLACE dough in bowl of a heavy-duty electric stand mixer; cool 5 minutes. Beat dough at medium speed with electric mixer using paddle attachment. Add eggs and egg whites, 1 at a time, beating until blended after each addition. (If desired, eggs and egg whites may be added 1 at a time and beaten vigorously with a wooden spoon instead of using the mixer.)
SPOON dough into a large heavy-duty zip-top plastic bag. (A large pastry bag may also be used.) Cut a 1 1/2-inch opening across one corner of the bag. Pipe 4-inch-long strips of dough 2 inches apart onto ungreased baking sheets.
BAKE at 425 degrees for 20 to 25 minutes or until puffed and golden. (Do not underbake.) Remove from oven, and cut a small slit in side of each eclair to allow steam to escape. Cool on wire racks.
SPLIT eclairs using a serrated knife, starting at 1 long side without cutting through opposite side. Pull out and discard soft dough inside.
CAREFULLY spoon about 1/4 cup Vanilla Pastry Cream into each eclair; close top of each eclair over filling. Top evenly with Chocolate Glaze. Chill eclairs for 2 hours or freeze up to 1 month.
VANILLA PASTRY CREAM: Whisk together first 4 ingredients in a 3-quart saucepan. Gradually whisk in half-and-half. Cook over medium heat, whisking constantly, until mixture comes to a boil. Cook 1 minute or until mixture is thickened and bubbly. Remove from heat; whisk in butter and vanilla. Cover and chill 4 hours.
CHOCOLATE GLAZE: Microwave morsels and whipping cream at HIGH in a 2-cup glass measuring cup 30 seconds to 1 minute or until melted, stirring twice. Whisk in butter until blended, and spoon immediately over eclairs.