• Set the oven to 350°F before preparing the mixtures. A fully heated oven gives the cake a consistent start.

Pecan Topping

• Whisk the melted butter, packed brown sugar, corn syrup, and salt together in a medium bowl. Stop when the sugar has begun to dissolve and no dry clumps remain, rather than waiting for every grain to disappear.
• Fold in the chopped pecans, then generously coat the bottom of the bundt pan with nonstick spray and immediately transfer the topping into it. The nuts should sit in a syrup-coated layer around the bottom, with the freshly applied spray helping the topping release later.

Cake Batter

• Mix the cake mix, eggs, vegetable oil, water, and sour cream in a large bowl, using a handheld mixer or mixing by hand. The batter should look evenly blended, with no visible pockets of dry cake mix or streaks of sour cream.
• Distribute the batter gently over the pecans with a spoon or scoop, then level the surface. Small additions disturb the topping less than one heavy stream, leaving an even cake layer over the nuts.
• Bake for 40 to 45 minutes at 350°F, checking the cake with a toothpick inserted into its thickest part. A few moist crumbs indicate doneness, while wet batter means the cake needs more baking.
• Move the pan to a cooling rack and start a 10-minute timer. This rest lets the crumb firm up while the brown sugar topping remains warm enough to release.
• At the timer, loosen the cake’s edges with a knife, gently tap and shake the pan, and turn it onto a cake plate before lifting the pan slowly. If nuts remain behind, remove them once comfortable to touch and press them onto the warm glaze, then let the cake cool completely.
• Cover the cooled cake for storage at room temperature or in the refrigerator, or wrap it tightly in several layers of plastic wrap for freezing. Wait until the cake is completely cool before enclosing it so trapped warmth does not create condensation.