Heat oven to 350 degrees F.
Grease a 9-inch springform pan with butter.
For graham cracker crust, crush graham crackers in food processor until consistency of bread crumbs; stir with melted butter until mixture holds shape when squeezed. If needed, add a little more melted butter.
Firmly press graham cracker “crust” into bottom and along bottom sides of spring form pan; set aside.
Sift together flour and sugar in small mixing bowl.
In medium bowl, stir together ricotta cheese and orange zest. Slowly fold in flour mixture with spatula until well blended and smooth.
Add eggs, one at a time, continuing to carefully fold with spatula. Stir in vanilla extract.
Pour batter into springform pan and gently smooth top with spatula.
Bake for 55-60 minutes at 350° F until cake is firm all the way to top center. Begin checking at 50 minutes. Cool completely and refrigerate for 2-3 hours to set. Begin checking at 50 minutes.
Dust top of cake with powdered sugar.
