In a saucepan, bring water and butter to a boil. Add flour all at once, stirring until a smooth ball forms. Remove from the heat; let stand for 5 minutes. Add eggs, one at a time, beating well after each addition. Continue beating until mixture is smooth. Drop by 1/4 cupfuls 3 inches apart onto greased baking sheets.

Bake at 400 for 30 minutes or until golden brown. Remove to wire racks. Immediately split puffs open and remove tops; discard soft dough from inside. Set puffs and tops aside to cool. For filling, combine sugar and cornstarch in a saucepan. Stir in milk and yogurt until smooth. Bring to a boil; cook and stir for 2 minutes or until thickened. Remove from the heat. Stir in lemon extract and butter flavoring. Cool. Fold in strawberries. Refrigerate until serving. Fill cream puffs; replace tops. Dust with confectioners' sugar.