Preheat oven to 325 degrees F. Mix cookie crumbs and butter and press into the bottom of a 9 inches springform pan. Set aside.
Combine cream cheese, sugar, flour, and Pure Lemon Extract. Mix well with an electric stand mixer with a paddle attachment, scraping bowl and beater often. Add sour cream, mix well. Add eggs, one at a time, mixing well after each addition. Pour into prepared pan. Bake approximately one hour and 15 minutes, or until center is almost set (it will jiggle slightly). Turn off oven and open the door. Run a knife around the edge of the pan, and allow the cheesecake to cool in the oven with the door open. Cool completely before removing from the pan. Store in the refrigerator.
In a saucepan, combine sugar, water, and Pure Lemon Extract. Cook, stirring, over medium heat until sugar is dissolved. Add cornstarch mixture and cook, stirring, until the mixture thickens slightly. While stirring the egg yolk, pour some of the hot sugar mixture into the yolks to temper them. Add the yolk mixture back into the saucepan and continue cooking and stirring until the mixture thickens. Add the butter and food coloring, if used, to make a bright yellow topping. Strain through a small sieve to remove any lumps. Cool to lukewarm, spread on cooled cheesecake and chill completely.
Preheat oven to 160 degrees C. Mix cookie crumbs and butter and press into the bottom of a 23 cm springform pan. Set aside.
Combine cream cheese, sugar, flour, and Pure Lemon Extract. Mix well with an electric stand mixer with a paddle attachment, scraping bowl and beater often. Add sour cream, mix well. Add eggs, one at a time, mixing well after each addition. Pour into prepared pan. Bake approximately one hour and 15 minutes, or until center is almost set (it will jiggle slightly). Turn off oven and open the door. Run a knife around the edge of the pan, and allow the cheesecake to cool in the oven with the door open. Cool completely before removing from the pan. Store in the refrigerator.
In a saucepan, combine sugar, water, and Pure Lemon Extract. Cook, stirring, over medium heat until sugar is dissolved. Add cornstarch mixture and cook, stirring, until the mixture thickens slightly. While stirring the egg yolk, pour some of the hot sugar mixture into the yolks to temper them. Add the yolk mixture back into the saucepan and continue cooking and stirring until the mixture thickens. Add the butter and food coloring, if used, to make a bright yellow topping. Strain through a small sieve to remove any lumps. Cool to lukewarm, spread on cooled cheesecake and chill completely.