Crumb Crust: Grind Oreos (filling and all) in food processor or crush in a bag. Combine cookie crumbs and butter. Press into the bottom and 2-inches up sides of 9-inch springform pan. Put in the freezer.
Chocolate Layer: Combine 8 oz of cream cheese and 1/4 sugar and beat until creamy. Add 1 egg and 1/4 tsp. vanilla; blend well. Stir in melted chocolate and 1/3 cup sour cream. Spoon over chocolate crumb layer.
Brown Sugar Layer: Combine 8 ounces of cream cheese, 1/3 cup brown sugar and flour and beat until well mixed. Add 1 egg and 1/2 tsp. vanilla; blend well. Stir in pecans. Spoon gently over chocolate layer.
White Sour Cream Layer: Combine 5 oz cream cheese and 1/4 cup sugar; beat until fluffy. Add egg and blend well. Stir in remaining 1 cup sour cream and vanilla. Spoon gently over praline layer.
Bake at 325 degrees for 1 hour; turn off oven and leave cheesecake in oven for 30 minutes; open door of oven and leave cheesecake in oven an additional 30 minutes. Let cool at room temperature for 1 hour, then chill for 8 hours or overnight.
Remove from pan and make one of the chocolate glazes listed.
Original Chocolate Glaze (which gets kind of hard, but tastes good): Combine 6 oz chopped semi-sweet chocolate and 1/4 cup butter in a small saucepan and melt over low heat. Remove from heat and stir in the 3/4 cup powdered sugar, 2 tablespoons of water and 1/4 teaspoon of vanilla until smooth. Pour over cake.
Alternative Glaze: Heat 1/3 cup of heavy cream and 1 tablespoon of corn syrup in a 2 cup microwave-safe glass measure until very hot but not quite boiling. Add 4 ounces of chopped chocolate (semisweet or dark) and stir until melted. At this point it will be rather thin, so let it sit for about 30 minutes or until it cools and thickens a bit, then pour it over the cheesecake.
At this point, the cake needs some sort of garnish. You could pile chocolate leaves on top, add nuts or do what I do and drizzle lines of melted white chocolate over the top.