• Preheat the oven to 350F (180C or 160C fan-forced).
• Wrap the outside of a 9-inch (23-cm) springform pan with aluminum foil. Wrap the pan at least 3-4 times so that the bottom and sides are covered, and that all seems are covered too.

Oreo Crust

• Crush the cookies (wafers and filling) in a food processor. Or place in a freezer bag and crush with a rolling pin. You want the cookies to be fine crumbs.
• Mix the crushed cookies with the melted butter.
• Press the mixture into the bottom of the pan, creating a slight lip around the edges.
• Bake in the preheated oven for 8 minutes. Remove from the oven and leave it turned on.

Cheesecake Filling

• In a very large bowl, beat together the cream cheese and sugar until smooth and creamy (about 2 minutes).
• Turn off the mixer and scrape down the sides of the bowl. Then mix in the sour cream.
• With the mixer still on a low speed, beat in the eggs 1 at a time until incorporated. Stop mixing when you no longer see pieces of eggs.
• Add the instant coffee to the Baileys and stir (it will partially dissolve). With the mixer on a low speed, slowly mix in the Baileys. Make sure the mixer is on a low speed - or the Baileys will splash up.

Baking & Cooling

• Place the springform pan in the middle of a large roasting pan (still wrapped in foil).
• Pour the cheesecake batter over the crust and smooth the top.
• Pour hot water into the roasting pan so that there's about 1 inch (2.5 cm) of water.
• Place the roasting pan in the oven (still at 350F from when you baked the crust). Bake for 50-65 minutes, or until the top looks set and when you gently nudge the pan it wobbles like jello or pudding. If it wiggles like a glass of milk, it's not done baking yet.
• Remove the roasting pan (with cheesecake inside) from the oven. Cool the cheesecake in the roasting pan until the water is room temperature.
• Remove the springform pan from the roasting pan and place on a wire rack. Continue cooling until it's room temperature.
• Cover the pan with aluminum foil and place in the fridge to chill for at least 6 hours or overnight.

Chocolate Topping & Serving

• Chop the chocolate into very fine pieces and place in a heatproof bowl.
• Heat the cream and Baileys (I poured them into 1 liquid measuring cup) until almost boiling. You can do this in the microwave or in a small saucepan over low heat while gently stirring.
• Pour the hot cream and Baileys over the chocolate. Let sit for 2-3 minutes, then whisk until smooth. If the chocolate hasn't quite melted, microwave on medium power (not high, which is default on many models) for 30-second intervals, whisking in between until smooth.
• Take the cheesecake out of the fridge. Trace around the edge with a thin, sharp knife. Then unclamp the outer ring of the springform pan.
• If there's condensation on top of the cheesecake, blot it off with a paper towel.
• Pour the ganache over the cheesecake, letting it drip over the edges. Return to the fridge until you're ready to serve.
• Slice the cheesecake with a sharp, thin knife (not a table knife). Be sure to slice all the way through the crust.