1. Get Ready! First, preheat your oven to 350°F (175°C) and lightly grease a 9-inch springform pan.
2. Whip Up the Crust: In a medium bowl, simply whisk together the crushed Oreo crumbs, sugar, and salt. Pour in the melted butter and stir with a fork until everything is evenly moistened, resembling soft, damp sand. Firmly press this mixture into the bottom and slightly up the sides of your prepared springform pan. Place it in the refrigerator while you prepare the filling so it can firm up nicely.
3. Craft the Creamy Cheesecake Filling: Using an electric mixer on medium-low speed, beat the softened cream cheese, sugar, flour, and a pinch of salt for about 3-4 minutes. Keep beating until the mixture is beautifully creamy and completely free of lumps. Scrape down the sides of the bowl, then add the heavy cream and vanilla extract, beating until just combined. Now, beat in the eggs and the egg yolk one at a time, mixing for about 15 seconds after each addition. Finally, gently fold in the cubed brownies by hand using a rubber spatula, ensuring they are well distributed throughout the filling.
4. Bake to Perfection: Pour your delightful cheesecake filling evenly over the chilled Oreo crust. Place the springform pan onto a rimmed baking sheet (this helps catch any potential drips and makes handling easier). Bake for approximately 40 to 55 minutes. The cheesecake is ready when the outer couple of inches look set and slightly puffed, but the center still has a gentle jiggle when you carefully move the pan.
5. Cool Down Slowly: Turn off the oven, crack the oven door open slightly, and leave the cheesecake inside for 1 hour to cool down gradually. This slow cooling process helps prevent cracks. After an hour, remove the cheesecake from the oven, place it on a wire rack, and run a thin knife around the edge of the cake. Allow it to cool completely to room temperature. Once cooled, refrigerate for at least 4 hours, or ideally, overnight, for the best firm and creamy texture.
6. Drizzle the Rich Ganache: When your cheesecake is perfectly chilled, it's time for the decadent topping! Place the finely chopped dark chocolate in a 4-cup measuring cup. In a small saucepan over medium heat, warm the heavy cream until it just begins to simmer (you’ll see tiny bubbles around the edges). Pour the hot cream directly over the chopped chocolate and let it sit undisturbed for 2 minutes to melt the chocolate thoroughly. Then, gently whisk from the center outwards until you have a thick, smooth, and glossy ganache.
7. Finish and Set: Pour the prepared ganache evenly over the top of your chilled cheesecake. If it's a bit thick, you can gently spread it with an offset spatula. Refrigerate for at least another 30 minutes to allow the ganache to set beautifully.
8. Chill and Enjoy! When ready to serve, carefully remove the sides of the springform pan and place the cheesecake on a serving platter. For neat slices, wipe your knife clean with a damp cloth between each cut. Savor every bite of this incredible, crowd-pleasing dessert!