Heat oven to 275 degrees.
Lightly grease bottom and side of 9 inch spring form pan with shortening.
Beat cream cheese and vanilla in medium bowl with electric mixer on medium speed until smooth.
Gradually beat in sugar until fluffy.
Beat in flour. Beat in eggs, one at a time.
Beat in chocolate until blended; pour into pan.
Bake about 1 hour 15 minutes or until center is firm.
Cool at room temperature 15 minutes.
Cover and refrigerate about 3 hours or until chilled.
Run metal spatula along side of cheesecake to loosen; remove side of pan.
Let cheesecake stand at room temperature 15 minutes before cutting.
Store covered in refrigerator.