Remove bottom of a 9 x 3-in. springform pan; wrap bottom with plastic wrap. Stir coffee, 2 Tbsp sugar and the Kahlúa in a shallow bowl until sugar dissolves. Set 1⁄2 the ladyfingers aside. For each of remaining ladyfingers, quickly dip one side into coffee mixture and place wet side up on pan bottom to cover, cutting ladyfingers as needed to fit. Freeze about 15 minutes until firm. Lift plastic wrap, with ladyfingers, off pan bottom and place on a flat plate in freezer. Heat oven to 325°F. Reassemble the springform pan and coat with nonstick spray. Quickly dip one side of reserved ladyfingers into coffee mixture. Place wet side up on pan bottom to cover, cutting ladyfingers to fit and pressing to fill spaces. Freeze until ready to fill. Beat cream cheese, 1 1⁄4 cups sugar and the cornstarch in a large bowl with mixer on medium speed until smooth. On low speed, beat in eggs, 1 at a time, just until blended. Beat in mascarpone and reserved 2 Tbsp coffee. Pour half the batter (3 cups) into pan; spread evenly. Top with ladyfinger layer from freezer; sprinkle with grated chocolate. Spoon on remaining batter; spread evenly. Bake 45 minutes, or until center still jiggles slightly when shaken. (Air bubbles may form on surface; they'll sink as cake cools.) Turn off oven (leave door closed); leave cake in oven 45 minutes. Carefully run a thin knife around the edge of the pan to release the cake (leave the pan sides on). Cool completely on a wire rack. Cover loosely; refrigerate at least 4 hours, preferably 1 day for best flavor. Note: Imported Italian savoiardi ladyfingers are crisp and longer than the familiar soft sponge cake variety.