separate five eggs, reserving whites and yolks separately. preheat oven to 350ºf. butter sides and bottom of a 9-inch spring form pan.
cream butter in a large mixing bowl using a mixer. add ½ cup sugar and mix well. reduce speed to medium. add two whole eggs and half the vanilla extract, scraping down sides occasionally. mix until sugar dissolves (4-5 minutes).
slowly add 1 2/3 cups flour. mix until dough starts to form a ball. remove from bowl. shape into a disc and wrap in plastic wrap.
refrigerate dough 1 hour.
roll out dough on lightly floured surface with rolling pin. press dough into spring form pan. spread apricot preserves on dough (bottom part only). cut ladyfingers in half lengthwise. arrange ladyfinger halves on top of preserves. set aside.
whip egg whites on high speed, gradually adding 1/3 cup sugar. mix until whites form soft peaks. place egg whites in separate bowl, set aside. zest lemon to yield ½ teaspoon lemon zest. whip egg yolks on medium speed for 1 minute. gradually add remaining sugar until dissolved and light in color. add drained ricotta cheese, remaining flour, salt, remaining vanilla extract, lemon zest and milk and gently fold until mixed.
gently fold in egg white mixture and spread egg and cheese mixture on top of dough. bake 60-70 minutes, or until lightly browned and a knife comes out clean. if cake starts to brown too quickly, tent with aluminum foil until done. remove from oven and cool at room temperature.