In bowl of stand mixer cream butter and sugar together until light and fluffy. Add eggs and vanilla and continue mixing until smooth.
Add flour mixture and milk in alternating amounts, starting and ending with flour. Stir until just blended.
Pour in springform pan. Bake for 25 minutes until center is set and toothpick comes out clean.
Lower oven temperature to 325*
In bowl of stand mixer beat cream cheese, sugar and vanilla together on medium-high speed until smooth.
Separately whisk eggs with a fork in a small bowl, add beaten eggs to cream cheese mixture on low until just combined. Stir in sour cream. Pour mixture over cake in the springform pan, spreading to cover.
Bake for 45-50 minutes until the outside edges appear set when gently shaken. Cool in pan on a wire rack for 15 minutes.
Loosen the edges of cake from the pan by running a butter knife around the cake.Allow cake to cool completely. Cover cake and chill for at least 4 hours (I chilled mine overnight)
When cheesecake is chilled heat heavy cream in a small saucepan until it almost comes to a boil. Remove from heat and stir in chocolate chips until melted. Stir in butter until smooth.
Chill for 15 minutes and then spread over top of cake.
Use a springform pan. This makes the entire process a lot easier. The sides will have to be greased well if it's not a good non-stick surface.If your cheesecake sticks to the pan, use a knife. The sides of my cheesecake did stick a bit to the sides, but running a knife along the inside of the pan before expanding the sides did the trick for easy release.Cool the chocolate before adding it to the cake. Once the chocolate mixture is completely blended, it needs to cool off a bit before spreading on the cake. You can drip some of the chocolate down the sides if you wish, but I chose to keep it all on the top.Store in the refrigerator or freezer. It should keep for up to 2 weeks in the refrigerator or up to 6 months when frozen.