Preheat oven to 350 degrees Fahrenheit.

Brownie Layer: Melt butter and chocolate chips and stir to combine. Remove from heat and whisk in sugar. Allow to cool for five minutes, stirring constantly. Add eggs and milk and whisk together. Stir in flour. Pour batter into a lined 10- x 16-inch pan. Bake for 30 minutes. After brownies are done, reduce oven temperature to 325 degrees Fahrenheit.

Cheesecake Layer: Beat cream cheese, sugar, eggs, vanilla sugar, and sour cream until smooth. Carefully pour over brownie layer.

Bake for an hour and a half or until center jiggles slightly. Chill.

Cookie Dough Layer: Cream butter and sugars until light and fluffy. Beat in milk and vanilla sugar. Add flour and salt and mix to form a dough. Stir in chocolate chips.

Spread cookie dough over cooked cheesecake with a spatula. Freeze until firm, then cut into thin rectangular slices. Drizzle additional melted chocolate over each individual slice, if desired.