Base: In a medium bowl, combine biscuit crumbs, sugar and melted butter. Mix well and press into the bottom and 2.5cm up the sides of a 22cm springform tin.
Caramel Filling: In a small saucepan, combine caramels with milk. Cook over low heat, stirring, until the caramels are melted and the mixture is smooth. Stir in chopped pecans. Pour the caramel-pecan mixture on to the crust and chill for 30 minutes.
Preheat oven to 165 degrees C.
In the top of a double boiler, heat chocolate, stirring occasionally, until chocolate is melted and smooth. Remove from heat and allow to cool until lukewarm. In a large bowl, beat cream cheese, sugar and vanilla until smooth. Beat in the eggs one at a time. Fold 1/3 of the filling into the melted chocolate, then pour the chocolate mixture back into the filling and mix until no streaks remain. Pour into crust.
Bake for 50 minutes, or until centre is almost set. Place a pan of water on the rack underneath cheesecake as it bakes to help keep it from cracking. Cool in oven with door open a little. Refrigerate for at least 5 hours before serving.