01 - Preheat oven to 340°F. Line bottom of 9-inch springform pan with parchment paper.
02 - Pulse graham crackers in food processor until finely ground. Mix in melted butter, sugar, and salt until combined. Press firmly and evenly into bottom of prepared pan. Bake for 10 minutes, then set aside to cool while preparing filling.
03 - In large bowl, beat Greek yogurt, cream cheese, and granulated sugar with electric mixer until completely smooth and creamy, about 2-3 minutes.
04 - Add eggs one at a time, mixing well after each addition. Stir in vanilla extract, lemon zest, lemon juice, cornstarch, and salt until fully incorporated and smooth.
05 - Pour filling over cooled crust. Smooth top with spatula. Bake for 50 minutes until center is just set but still slightly wobbly when gently shaken.
06 - Turn off oven and crack door open slightly. Let cheesecake cool inside oven for 1 hour. Remove and cool completely to room temperature, about 1 additional hour.
07 - Refrigerate cheesecake for at least 4 hours, preferably overnight, until completely set and cold throughout.
08 - In small bowl, whisk together sour cream or Greek yogurt, powdered sugar, and vanilla until smooth. Spread evenly over chilled cheesecake before serving.
09 - Slice cheesecake with sharp knife dipped in hot water, wiping clean between cuts for clean edges. Serve chilled.