Step 1: Preheat your oven to 325°F (165°C). Lightly grease a 9-inch springform pan.
Step 2: In a medium bowl, combine 1½ cups of pecan shortbread cookie crumbs, 2 tablespoons of brown sugar, and ¼ cup of melted butter. Mix until well combined and the crumbs are moistened.
Step 3: Press the crumb mixture firmly and evenly into the bottom of the prepared springform pan.
Step 4: Bake the crust for 10 minutes until lightly golden. Remove from the oven and let it cool completely on a wire rack.
Step 5: In a large mixing bowl, combine 1 box of red velvet cake mix, 1 cup of buttermilk, ½ cup of vegetable oil, and 3 large eggs.
Step 6: Beat the mixture with an electric mixer on medium speed for 2-3 minutes until smooth and lump-free.
Step 7: Carefully pour half of the red velvet batter over the cooled pecan crust in the springform pan. Gently tap the pan on the counter a few times to evenly distribute the batter and release any air bubbles. (Reserve the remaining half of the batter for another use, such as cupcakes, or discard.)
Step 8: In a separate large bowl, beat 16 oz of softened cream cheese with ½ cup of granulated sugar until the mixture is completely smooth and creamy, without any lumps.
Step 9: Add 2 large eggs, one at a time, beating on low speed after each addition just until combined. Avoid overmixing once the eggs are added, as this can introduce too much air and lead to cracks.
Step 10: Stir in 1 teaspoon of vanilla extract until fully incorporated.
Step 11: Gently spoon the cheesecake mixture over the red velvet cake layer in the springform pan. Use an offset spatula to carefully spread and smooth the top evenly.
Step 12: Bake the cheesecake in the preheated oven at 325°F (165°C) for 50-60 minutes, or until the edges are set but the center still has a slight jiggle.
Step 13: Once baked, turn off the oven, crack the oven door slightly, and allow the cheesecake to cool inside for 1 hour. This slow cooling prevents drastic temperature changes that can cause cracks.
Step 14: Remove the cheesecake from the oven and let it cool completely on a wire rack at room temperature. Then, transfer it to the refrigerator to chill for at least 4 hours, or preferably overnight, before adding the topping.
Step 15: In a small saucepan over medium heat, melt ¼ cup of butter.
Step 16: Stir in ½ cup of brown sugar and cook, stirring constantly, until the sugar dissolves and the mixture begins to bubble.
Step 17: Remove from heat and stir in 2 tablespoons of heavy cream, ½ cup of chopped pecans, and ¼ teaspoon of salt.
Step 18: Return the saucepan to medium-low heat and simmer for 2-3 minutes, stirring constantly, until the topping slightly thickens.
Step 19: Remove from heat and let the butter pecan topping cool slightly before pouring it evenly over the thoroughly chilled cheesecake.