Follow these detailed instructions carefully to ensure your dessert squares turn out perfectly. Patience, especially during the chilling phase, is key to success.

Part 1: Preparing the Crust and Pan

1. Preheat and Prepare: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on the two long sides. This “sling” will make it incredibly easy to lift the entire block of dessert out of the pan for clean cutting later. Lightly grease the parchment paper and any exposed sides of the pan.
2. Mix the Crust Ingredients: In a medium bowl, combine the graham cracker crumbs, finely chopped pecans, light brown sugar, and ground cinnamon. Stir until everything is evenly distributed.
3. Add the Butter: Pour the melted unsalted butter over the crumb mixture. Use a fork or your fingertips to mix until all the crumbs are moistened and the mixture resembles wet sand.
4. Press and Bake: Transfer the mixture to your prepared baking pan. Press it down firmly and evenly across the bottom of the pan. You can use the bottom of a flat measuring cup to help create a compact, even layer. Bake the crust for 10 minutes. This pre-baking step, known as blind baking, helps the crust set and prevents it from becoming soggy under the creamy filling. Once baked, remove it from the oven and set it on a wire rack to cool slightly while you prepare the filling.

Part 2: Creating the Velvety Filling

1. Beat the Cream Cheese and Sugars: In a large mixing bowl, using a handheld electric mixer or a stand mixer fitted with the paddle attachment, beat the softened cream cheese on medium speed until it is completely smooth and creamy, with no lumps. This step is crucial for a silky final texture. Scrape down the sides and bottom of the bowl. Add the granulated sugar and light brown sugar and beat again until well-combined and fluffy, about 2 minutes.
2. Incorporate the Sweet Potato: Add the mashed sweet potato to the cream cheese mixture and beat on low speed until just combined. Be careful not to overmix here.
3. Add Eggs and Liquids: Add the room temperature eggs one at a time, beating on low speed after each addition just until the yolk disappears. Overbeating after adding eggs can incorporate too much air, which can cause the filling to puff up and then crack as it cools. After the eggs are in, mix in the heavy cream and vanilla extract.
4. Mix in the Spices: Add the ground cinnamon, nutmeg, ginger, and cloves. Mix on the lowest speed for about 15-20 seconds, just until the spices are incorporated. Scrape the bowl one last time to ensure everything is homogenous.

Part 3: Assembling and Baking

1. Pour the Filling: Pour the prepared sweet potato filling over the slightly cooled, pre-baked crust. Use a spatula to spread it into an even, smooth layer, making sure it reaches all the corners of the pan.
2. Prepare the Streusel (If Using): In a small bowl, whisk together the all-purpose flour, chopped pecans, brown sugar, and cinnamon. Add the cubes of cold butter. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter remaining.
3. Top and Bake: Sprinkle the streusel topping evenly over the sweet potato filling. Carefully place the pan in the preheated oven. Bake for 45 to 55 minutes. The dessert is done when the edges are set and the center has a slight jiggle to it (it should not be liquidy, but will not be rock solid either). It will continue to set as it cools.
4. Cool Completely: Remove the pan from the oven and place it on a wire cooling rack. Let it cool at room temperature for at least one hour. The pan will still be warm.
5. Chill for Best Results: Once mostly cool, cover the pan loosely with plastic wrap or foil and transfer it to the refrigerator. Chill for a minimum of 4 hours, but preferably overnight. This chilling period is non-negotiable! It allows the filling to fully set, making for a perfectly creamy texture and allowing for clean, beautiful slices.