Pour the graham cracker crumbs into a medium bowl. Sift the powdered sugar over the crumbs and toss to combine.

Melt the butter in a small saucepan over medium heat.

Stir the melted butter into the graham crackers until evenly moistened. Scrape the crumbs into the 12" Skillet.

Firmly and evenly press the crumbs onto the bottom of the pan with the palm of your hand. (Do not go up the sides.)

Cook the crust over low heat for 5 minutes to set it. Set aside to cool.

Combine the sugar, cream cheese, ricotta cheese, yogurt, lemon juice, flour and vanilla in the bowl of a food processor. Puree, scraping down the sides of the bowl once or twice until the mixture is completely smooth.

Pour in the egg whites and eggs and puree until smooth. Pour the mixture into the cooled, crust-lined pan.

Cover and cook over low heat for about 1 hour and 15 minutes until the center is just barely set when the pan is gently shaken.

Remove the pan from the heat and let the cheesecake stand covered for 15 to 20 minutes.

Refrigerate uncovered for at least 2 hours until the cake is completely cold and firm. Slice in to wedges and serve.