Preheat oven to 350°F. Grease a 9-inch springform pan and line the bottom with parchment paper. Allow the parchment paper to hang outside of the springform pan. This makes it easier to remove the cheesecake.
For the crust, combine graham cracker crumbs, almonds, coconut flakes, cocoa powder, and brown sugar in a medium sized bowl. Stir in melted butter. Pour into the bottom of the springform pan and pat into the bottom and up the sides of the pan. Bake for 10 minutes and then let the crust cool on a wired rack while you make the filling.
Reduce the oven temperature to 300°F. Beat cream cheese and brown sugar together in a large mixing bowl. Mix in flour and sour cream, stopping to swipe down the sides and bottom of the bowl when needed. Mix until just combined. Do not over mix.
Mix in the eggs, one at a time, until combined. Mix in vanilla extract and custard powder.
Pour the cheesecake filing into the springform pan, over the crust. Cover the outside of the springform pan with aluminum foil. Tie a crock pot liner around the pan, over top of the aluminum foil. This helps from water seeping into the cheesecake.
Place the springform pan into a larger baking pan or casserole dish. Fill the larger pan with water to go halfway up the side of the springform pan. Place this on the middle rack of the oven and bake for 1 hour, 20 minutes. Do not open the oven until it is done. Opening the oven causes the temperature to change drastically and can make the cheesecake crack. After the time is done, the cheesecake will still be a bit jiggly in the center.
Turn off the oven and let the cheesecake cool in the turned off oven with the oven door closed for 30 minutes. Crack the door of the oven open and keep the cheesecake in the turned off oven for another 30 minutes. This helps the cheesecake cool down slowly so that it won't crack.
Take the cheesecake out of the oven and run a knife between the crust and springform pan. When the cheesecake cools, it contracts and the crust can now move with the cheesecake. Let it sit at room temperature for 20 minutes and then cover the cheesecake in the springform pan and transfer to the refrigerator. The cheesecake needs to cool for at least 2 hours or overnight.
To make the chocolate ganache, heat heavy whipping cream in the microwave or in a small saucepan over medium heat, until it is hot, but not boiling. Pour the heavy whipping cream over the chocolate. Let it sit for 3 minutes, and then whisk until smooth. Remove the cheesecake from the refrigerator and unmold it from the springform pan. Place it on a cake stand or serving plate and pour the chocolate ganache over the top. Spread the ganache evenly and return the cheesecake to the refrigerator to cool the ganache.
To make the whipped topping, combine heavy whipping cream, powdered sugar, and vanilla extract to a large mixing bowl. Whisk until stiff peaks. Remove the cheesecake from the refrigerator and pipe the whipped topping on top. Scatter slivered almonds on top of the cheesecake.
Store the cheesecake covered in the refrigerator for up to 5 days.