Preheat oven to 350 degrees F. Butter an 8-inch round cake pan.
In a small saucepan, bring 1 1/2 cups water to a boil. Drizzle the semolina into the water, stirring constantly with a wooden spoon. Stir in 1/4 cup of the sugar. Cook, stirring often, until thickened, about 4 minutes. Remove the pan from the heat and let cool slightly.
In a large bowl, whisk the ricotta, egg yolks, liqueur, and zest. Stir in the raisins.
In a large bowl, beat the egg whites with salt on low speed until foamy. Gradually beat in the remaining 1/4 cup sugar on high speed and beat until the whites hold stiff peaks.
With a spatula, gently fold the egg whites into the ricotta mixture. Scrape the mixture into the prepared pan.
Bake the cheesecake for 1 hour or until puffed and golden on top. Remove from the oven. Let cool on a rack for 10 minutes. Invert onto a plate and let cool.
Serve at room temperature or chilled, sprinkled with confectioners' sugar.
Recipe courtesy of Italian Holiday Cooking (Morrow, 2001) by Michele Scicolone