Place ricotta in a sieve lined with cheesecloth, place in refrigerator, and let the ricotta drain for several hours or overnight.
Preheat the oven to 350 degrees. Fit a parchment circle into the bottom of a 7-inch springform pan. Make crust: Combine graham-cracker crumbs and 2 tablespoons sugar in a small bowl. Stir in melted butter with a fork until crumbs are moistened. Press into bottom of pan, and bake for 10 minutes.
Place lemon juice in a small bowl, and sprinkle gelatin over the surface. Set aside for 10 minutes to soften.
In a small, heavy saucepan, beat egg yolks until smooth. Whisk in milk. Gradually whisk in remaining 1/2 cup plus 2 tablespoons sugar. Add salt. Cook over low heat, stirring constantly, until mixture coats the back of a spoon, about 7 minutes. Do not allow to boil. Transfer to a bowl, and stir.
Stir in softened gelatin, orange zest, and vanilla, mixing until gelatin is completely dissolved. Set custard aside.
Place drained ricotta in the bowl of a food processor and process until smooth. Add cream cheese and process again until smooth. With machine running, add warm custard and process just long enough to combine. Transfer to a bowl and fold in whipped cream. Pour mixture into the prepared pan, cover, and chill overnight.
Place a candied orange slice in center of cake. Pour glaze over top, tipping cake pan to cover completely. Chill for 1 hour, or until glaze is set.
To unmold, wrap a hot towel around sides of pan to help release cake, and run a thin knife around the inside of the pan. Carefully remove outside of pan. Slide onto a serving plate, and chill until ready to serve.