Preheat oven to 350 degrees F.
Grease sides and bottom of pans.
Do not follow cake mix instructions from the box. Add the dry cake mix together with oil, water, eggs, sour cream and pudding mix. Beat with an electric mixer on low for 30 seconds and then medium speed for 1-2 minutes. Pour batter into two 8" or 9" baking pans, sprayed with nonstick cooking spray or lined with parchment paper.
Bake for 30-35 minutes (or until a toothpick inserted comes out clean). Baking time may vary based on size of pan.
Crush Oreo cookies (best with food processor) and stir in cream cheese until fully blended. This will be a very thick "filling".
After cake has cooled, spread Oreo filling between layers as you stack. Again, it's very thick so you might have to use your hands to help spread it onto cake.
In a saucepan over medium heat, melt together butter, sugar, and evaporated milk.
Bring to a rolling boil for 1 minute and stir in chocolate chips.
Remove from heat and pour over cake (fudge sets up quickly) and garnish with extra chocolate chips!