• Start by preheating your oven to 350°F. Give a 9-inch springform pan a light coat of cooking spray and set it aside for later.
• Pop your chocolate sandwich cookies and hazelnuts into a food processor and pulse until everything’s finely crushed. Pour in the melted butter and pulse again until the mixture looks like wet sand. Scoop the crust mixture into your prepared pan, then use the back of a measuring cup to press it down firmly into the bottom and slightly up the sides. Try to make it nice and even! Bake the crust for 10 to 12 minutes, then take it out and let it cool on a wire rack. Keep your oven on—we’re not done yet!
• To make the filling, melt 10 ounces of chopped chocolate using a double boiler, stirring now and then until it’s smooth and silky. Don’t have a double boiler? No problem! Just microwave the chocolate in a medium microwave-safe bowl in 30-second bursts, stirring in between, until melted. Once it’s melted, set it aside to cool down for at least 10 to 15 minutes—you want it at room temperature before it joins the cheesecake party.
• In the bowl of a stand mixer, beat together the cream cheese, Greek yogurt, and sugar on medium-low speed for about a minute, just until smooth. The key here is not to overmix—gentle and slow is the way to go.
• Next, sprinkle in the cocoa powder and salt. Mix again on medium-low speed until everything’s well blended. Don’t forget to scrape down the sides of the bowl as you go! Now, add the eggs one at a time, mixing each one in on medium-low until just combined. Give the bowl one more scrape down.
• Finally, pour in that cooled, melted chocolate and mix on low speed until it’s fully combined and the batter looks dreamy.
• To prep for baking, double-wrap the bottom and sides of your springform pan (with the crust inside) with foil. Set the whole thing into a large roasting pan or any bigger dish that can hold it. Pour the chocolate cheesecake filling over the cooled crust and smooth the top with a spatula.

To make a water bath:

• Boil a big pot of water—or use a kettle to make things easier. Once your water’s bubbling hot, slide the roasting pan with your cheesecake into the center rack of the oven. Then, carefully (and slowly!) pour the hot water into the roasting pan. It should come about 1 inch up the sides—this helps keep things steamy so the cheesecake bakes evenly and stays moist. A kettle makes this part much easier to handle! Once the water’s in, gently push the oven rack back in and close the door.
• Bake your cheesecake for about 1 hour to 1 hour and 15 minutes, until the center is just set and looks slightly dry. A little jiggle in the middle is totally fine! And don’t panic if it cracks while baking—we’ll be covering it with ganache anyway, so no one will know!
• When the time’s up, turn off the oven and crack the door open, but leave the cheesecake inside. Let it hang out for 30 minutes to an hour. This slow cooldown helps prevent any sudden temperature changes that might cause cracks.
• After it’s had time to chill out, carefully take the roasting pan out of the oven and transfer the springform pan to a wire rack. Leave the cheesecake in the pan for now—just run a knife around the edge to loosen the crust. Then pop it in the fridge to chill for at least 4 hours (but overnight is even better for the perfect texture!).
• Once it’s nice and cold and you’re ready to top it, go ahead and remove the cheesecake from the pan. You're almost there!

To make the chocolate hazelnut ganache:

• In a medium saucepan, warm the heavy cream over medium-low heat—just until it’s nice and hot, not boiling. Stir in the chocolate hazelnut butter and keep stirring until the mixture is smooth and dreamy. Now toss in the chopped dark chocolate and stir until it’s fully melted and everything is beautifully combined. Once it’s silky and smooth, take it off the heat.
• Pour the ganache right into the center of your chilled cheesecake, then use a spatula or the back of a spoon to gently spread it out to the edges. Sprinkle the top with chopped toasted hazelnuts and a pinch of sea salt for that perfect finish. Let the ganache set for about 10 minutes at room temp.
• You can slice and serve it right away—or pop it back in the fridge to enjoy later. Just a heads-up: the cheesecake tastes best within 2 to 3 days, since the crust gets softer over time. Cut into 12 to 16 slices and dig in—enjoy every bite!