Mix graham cracker crumbs with the butter until thoroughly combined and press into the bottom of a 9-inch springform pan. Place the pan on a baking sheet and bake for 8-10 minutes; remove to cool. Reduce oven heat to 325F.
Place the cream cheese in a large bowl; add the sugar substitute and flour. Using an electric mixer beat until smooth. Add the vanilla and mix until well blended and then beat in the eggs one egg at a time, and then add in the milk, mixing until well blended. Spoon mixture onto the crust in the springform pan.
The separate ½ cup of the cheese mixture into a small bowl, add the dulce de leche and using a spoon mix until well blended. Place tablespoons of the mixture over the batter and gently swirl it in with the edge of a knife or spatula.
Bake at 325 for 45 – 55 minutes or until center is almost set. Remove from the oven and run a knife around the edge to help keep the cheesecake from cracking.
Cool for 20 minutes, cover, and chill for at least 6 hours before serving.