Preheat oven to 350° F. Spray a 9×13 glass pan with nonstick cooking spray and set aside.: When the oven reaches 350° F , you will notice a steady warm breath as you open the door, signaling the environment your custard needs to set evenly. Preparing a 9×13 glass baking dish with nonstick spray prevents sticking and helps the edges brown gently; glass also shows visual cues as the bottom cooks. Avoid skipping the spray, because a sticky corner can ruin neat slices and make serving difficult. If your oven runs hot, rotate the pan halfway through baking to maintain even color.
In a large bowl, whisk pumpkin, sugar, pumpkin pie spice, salt, eggs and evaporated milk together until completely smooth. Pour into the bottom of prepared pan.: As you whisk, the mixture will transform from separate components into a glossy, uniform custard with the warm aroma of pumpkin pie spice rising. The whisking action incorporates air and helps dissolve the granulated sugar , which aids even setting. Pouring into the pan should reveal a satiny surface free of lumps, which indicates proper mixing. One common mistake is underwhisking, which leaves streaks of egg or dry pockets of spice, so take the extra minute to achieve smoothness.
Sprinkle with cake mix evenly and gently press to flatten the top. Sprinkle with chopped pecans and drizzle with melted butter.: When the yellow cake mix is evenly dusted across the pumpkin, it creates a dry layer that will absorb some liquids and crisp as it bakes. Lightly pressing ensures good contact without compacting the topping. Adding toasted, chopped pecans distributes crunchy pockets throughout, and the drizzle of melted butter helps the mix brown into a golden crust. A misstep here is dumping the cake mix in one clump, so take time to scatter it evenly for consistent texture.
Bake 60-80 minutes or until cake is completely set. Start checking at 60 minutes to ensure you don't over bake. Cool 10 minutes before cutting and serving with ice cream or whipped cream. Drizzle with caramel sauce if desired.: While baking, listen for a gentle bubbling at the edges and watch for the center to lose its glossy sheen; these are signs the custard is approaching set. The top should be golden, and a knife inserted near the center will come out mostly clean with a few moist crumbs. Over baking can lead to a dry filling, so begin checking at 60 minutes and tent with foil if the edges brown too quickly. A common error is trusting timing alone rather than watching visual cues, so rely on texture and color as your guide.
Cool 10 minutes before cutting and serving with ice cream or whipped cream. Drizzle with caramel sauce if desired: After removing from the oven, the pan will give off a warm, spicy steam and the top will crisp as it rests. Cooling for about 10 minutes allows the custard to firm up so slices hold together. Serving warm enhances aroma and mouthfeel, and a scoop of cold whipped cream or a drizzle of caramel sauce creates contrast between warm custard and cool toppings. Be careful not to cut too soon, because the hot filling can crumble and make messy servings; patience yields cleaner slices and better texture.