Using a food processor, crush lemon sandwich cookies into small crumbs. Press along with melted butter into bottom of a 9" springform baking pan. Bake for 8 minutes at 350 degrees. Let cool.
In mixer, beat cream cheese, sweetened condensed milk and flour on low until smooth. Mix in sour cream, lemon juice and lemon extract. Beat in eggs one a time. Stir in blueberries. Pour over chilled graham cracker crust in pan.
Bake at 300 degrees for 1 hour, 15 minutes. Turn off oven, crack door and leave cheesecake in cooling oven for 1 hour. Remove to counter, cooling completely. Refrigerate several hours or overnight.
In saucepan on stove, heat sugar and lemon juice. Add blueberries; cook about 5-7 minutes or until blueberries release juice. Mix together cornstarch and water in small bowl, then add to blueberry mixture, stirring constantly until mixture reaches desired thickness. Let cool completely. Pour over entire cheesecake or spoon over each individual slice.