In a small bowl, cut butter into flour until crumbly. Stir in pecans. Press onto the bottom of four 6-oz. custard cups coated with cooking spray. Bake at 350° for 14-16 minutes or until lightly browned. Cool completely on a wire rack.
In a small bowl, beat the cream cheese and confectioners' sugar until fluffy; fold in whipped topping. Spoon over crusts. Cover and chill. In a small saucepan, combine the sugar, cornstarch, salt and water until smooth. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove from the heat.
Stir a small amount of hot filling into egg; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from the heat.
Gently stir in the vinegar, lemon juice, butter and lemon extract. Cool to room temperature without stirring. Spread over cream cheese layer. Chill for 4 hours or overnight. Top with whipped topping if desired. Yield: 4 servings.