Grease a 9” springform pan and line the bottom with parchment paper. Set aside.

Preheat the oven to 325°F.

In the bowl of a food processor, pulse Oreo cookies until fine crumbs form. (you can also crush cookies in a ziploc bag using a mallet or rolling pin.)

Stir or pulse in melted butter until evenly combined.

Press cookie crumb mixture into the bottom and at least halfway up the sides of the springform pan. This will make a thick Oreo cookie crust. Set aside.

In a large mixing bowl, beat the cream cheese until light and fluffy (using a hand mixer or standing mixer works well.)

Add 1 ½ cups of granulated sugar and continue beating until combined.

Add flour, vanilla, Bailey’s, heavy cream, and sour cream and stir until combined.

By hand, mix in the eggs, one at a time. Be careful not to overmix or stir too much air into the batter (which can lead to extra rising and cracking of the cheesecake.)

Gently spread the cheesecake mixture into the prepared Oreo crust.

Wrap the springform pan in TWO LAYERS of aluminum foil (to prevent water from getting in) and place the pan into a larger heat-proof pan that can hold water at least 1” up the sides of the pan.

Fill with the exterior pan with water to create a water bath for the cheesecake. Alternately, you can place a pan of water on the rack under the cheesecake while it cooks in the oven.

Bake for approximately 75 minutes. The cheesecake should appear matte across the top. Around the edges of the cheesecake should be set, but the center will be jiggly when you shake it gently. After 75 minutes, turn off the oven, keeping the door closed for 20 minutes. After this 20 minutes, crack the oven door and leave the cheesecake in place for another 20 minutes to continue cooling slowly.

Remove the cheesecake from the oven. Allow to cool to room temperature and then chill in the refrigerator for at least 3 more hours.

To make the ganache, heat the heavy cream in the microwave or a small saucepan until simmering. Pour over the chocolate chips and cover the container with a plate or lid to trap the heat. After 3-5 minutes, whisk the cream/chocolate mixture until a smooth ganache forms.

Pour the ganache over the chilled cheesecake and spread until it begins to drip over the edges. Allow ganache to set - about 15 minutes.

Just before serving top with whipped cream and dust with cocoa powder, if desired.