Choux paste is the French name for this tender pastry; we've simplified it by using piecrust mix.
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° 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 éclairs 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 éclair; close top of each éclair over filling. Top evenly with Chocolate Glaze. Chill éclairs for 2 hours or freeze up to 1 month.
Peanut Butter-Chocolate Éclairs: Follow recipe for Vanilla Cream-Filled Éclairs, substituting Peanut Butter Pastry Cream for Vanilla Pastry Cream.
Banana-Chocolate Éclairs: Follow recipe for Vanilla Cream-Filled Éclairs, adding 3 medium bananas, quartered lengthwise and thinly sliced, to Vanilla Pastry Cream after chilling 4 hours.
Mocha Éclairs: Follow recipe for Vanilla Cream-Filled Éclairs, substituting Coffee Pastry Cream for Vanilla Pastry Cream.
Strawberry Cream Éclairs: Follow recipe for Vanilla Cream-Filled Éclairs, substituting Grand Marnier Pastry Cream for Vanilla Pastry Cream. Slice 1 quart strawberries, and spoon evenly into éclairs before filling with pastry cream. Top with White Chocolate Glaze; drizzle with Chocolate Glaze.