1 cup butter, softened
1 cup packed light brown sugar
3 egg whites
2 3/4 cups milk
2 tablespoons lemon extract
1 1/2 teaspoons vanilla extract
1 1/2 teaspoons cornstarch
1 1/2 cups chopped cognac
In a small saucepan, mix sugar, butter, brown sugar and egg white; heat over medium-low heat, stirring constantly, until sugar is dissolved. Remove from heat and whisk in milk, lemon extract, lemon extract, cornstarch, and cognac. Transfer to a large bowl, crushing ice cream with spoon.
Combine crushed ice cream and remaining lemon zest in small bowl. Pour mixture into pastry shell and chill overnight.