• Preheat the oven to 350F degrees.
• Wrap the outside of a 9-inch springform pan in aluminum foil. Wrap it at least 3 times so that the bottom and up the sides are covered, and there are no seams showing.

Oreo Crust

• Blitz the Oreo cookies in a food processor until they're crushed cookie crumbs.
• Add in the melted butter and pulse a few times to combine.
• Press the mixture into the bottom and slightly up the sides of the prepared pan.
• Bake the crust in the preheated oven for 10 minutes. (Leave the oven turned on).

Baileys Cheesecake Filling

• Beat the cream cheese until soft, then beat in the sugar.
• Sift in the cocoa powder and cornstarch, then beat in the sour cream. Turn off the mixer and scrape down the sides of the bowl.
• With the mixer on low speed, beat in the eggs 1 at a time.
• Fold in the Baileys using a large rubber spatula.

Baking and Cooling the Cheesecake

• Pour the cheesecake batter on top of the crust and smooth the top.
• Place the cheesecake pan (still wrapped in aluminum foil) in the middle of a large roasting pan.
• Pour about 1/2 - 1 inch of hot water into the roasting pan so that the cheesecake is surrounded by water (this is your water bath).
• Place the roasting pan with the cheesecake inside in the oven and bake for 55-65 minutes, or until the top looks just set, but the cheesecake still has a slight wobble in it.
• Remove from the oven and let the cheesecake cool to room temperature (while still in the water bath).
• Remove the cheesecake pan from the water bath, cover lightly, and place in the fridge to chill for at least 6 hours before serving.

Chocolate Ganache

• Chop the chocolate into very small pieces and place in a glass, heatproof bowl.
• Add the cream to a small saucepan over medium heat, and heat the cream to a gentle simmer while stirring.
• Pour the hot cream over the chopped chocolate and let sit for 1-2 minutes.
• Whisk the mixture until smooth, then whisk in the Baileys. If the chocolate isn't fully melted, heat in the microwave for 30 seconds on medium heat.

Serving

• Remove the cheesecake from the fridge.
• Gently trace around the edge of the cake with a thin, sharp knife. Unclamp the springform.
• Drizzle the ganache over the cake, and optionally top with whipped cream.