CHEESECAKE: Position racks in center & lower third of oven. Place large roasting pan on lower rack; fill halfway with water. Preheat oven to 325 degrees F. Coat 9" springform pan with cooking spray. Line bottom of pan with buns, cut size down.
On medium high speed, beat cream cheese & sugar until light & fluffy, 2 - 3 minutes. Beat in eggs, one at a time. Add sour cream, flour & vanilla; beat until combined. Pour over buns in pan. Bake on center rack 1 hour or until center jiggles slightly. Turn oven off. Leave cheesecake in oven with door closed 1 hour. Remove & cool completely on rack. Refrigerate overnight.
TOPPING: On medium high, beat cream cheese & butter until blended, 1 - 2 minutes. Gradually beat in sugar, then milk until light & fluffy, 2 - 3 minutes. Reserve.
DRIZZLE: In small microwave safe bowl, mix brown sugar, butter & cinnamon until blended. Microwave on HIGH in 15 second intervals, stirring, until mixture is melted & smooth.
Spread topping over cheesecake top. Pipe thin line of drizzle in concentric circles over topping. Using toothpick, pull lines through drizzle, alternating directions, to create pattern.