Place a greased 10-in. springform pan on a double thickness of heavy-duty foil (about 18 in. square). Securely wrap foil around pan.
In a food processor, combine graham crackers and pecans; cover and process until fine and crumbly. Stir in butter. Press onto the bottom of prepared pan. Chill for 30 minutes.
In a large bowl, beat cream cheese and sugar until smooth. Beat in the sour cream, flour, milk and vanilla. Add eggs, beating on low speed just until combined. Pour over crust. Place springform pan in a large baking pan; add 1 in. of hot water to larger pan.
Bake at 325° for 75-80 minutes or until center is almost set and top appears dull. Remove springform pan from water bath. Cool on a wire rack for 10 minutes. Carefully run a knife around edge of pan to loosen; cool 1 hour longer. Chill.
For topping, in a small heavy saucepan over medium-low heat, combine sugar and water. Cook, stirring occasionally, until sugar begins to melt. Cook without stirring until dark reddish brown, about 15 minutes.
Reduce heat to low; gradually whisk in cream. Cook and stir over medium heat until a candy thermometer reads 225°. Remove from the heat; stir in butter and vanilla. Cool to room temperature.
Spread topping evenly over cheesecake (do not scrape sides of pan). Garnish with pecan halves. Refrigerate overnight. Remove sides of pan. Yield: 12-14 servings.