Place rack in the center of the oven then preheat to 325 degrees. In a small bowl, mix cracker crumbs with non-fat yogurt. Use a spoon to mix until well combined, and then use your fingers to evenly distribute the yogurt through the crumbs—the mixture should feel like damp sand and hold together when compacted.
Press the crumb mixture into the bottom of a 9" spring-form pan, allowing some of the crust to come up the sides of the pan. Bake 5–6 minutes then remove from oven to cool.
In a large bowl, or the bowl of a stand mixer, beat cream cheese until smooth. Add Splenda to the mixture then beat until combined. Add flour, lemon zest, vanilla, egg whites, whole eggs and sour cream then beat again until perfectly smooth, scraping the sides as necessary to ensure everything is incorporated.
Pour batter into the cooled crust, place the spring-form pan on a baking sheet, and then return to oven. Bake 25–30 minutes or until the edges are set and the center is still slightly wobbly.
Remove from oven then let cool completely before removing from pan. Cover and chill for 2 hours, slice and serve.
Notes
We served ours with a bit of fresh strawberries with a sprinkle of sugar, but this cake is yummy all by itself!