Preheat your oven to 350°F. Generously grease the bottom and sides of a solid 9-inch round cake pan with butter or non-stick baking spray, then line the bottom with a circle of parchment paper for a flawless release.

In a small saucepan set over medium-low heat, combine the 1 stick of unsalted butter, packed brown sugar, corn syrup (or alternative syrup), cinnamon, and a pinch of salt. Stir frequently for 2 to 3 minutes just until the butter completely liquefies and the sugar crystals dissolve into a smooth, uniform liquid paste. Do not let the mixture bubble or boil down too long.

Pull the saucepan from the heat source and stir in the chopped pecans to coat them thoroughly in the hot caramel sauce. Pour the mixture directly into the bottom of your lined cake pan, smoothing it with a spatula into a flat, tight, and even layer, then set the pan aside.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until light and evenly combined.

In a separate large mixing bowl, beat the 2 large eggs and granulated white sugar together with an electric hand mixer on high speed for 1 to 2 minutes until the mixture turns pale yellow and thickens slightly.

Reduce the mixer speed to low and slowly stream in the neutral vegetable oil, sour cream, whole milk, and vanilla extract, blending continuously until the wet ingredients form a smooth, fully emulsified baseline.

Switch to a silicone spatula and add the dry flour mixture to the wet bowl. Fold gently just until the white pockets disappear and a thick, smooth batter forms; over-mixing at this stage creates tough gluten grids that will ruin the delicate cake texture.

Spoon the cake batter gently in dollops over the pecan layer in the pan, then use your spatula to smooth the top into a flat, level sheet without disturbing the nuts underneath.

Place the pan on the middle oven rack and bake at 350°F for 35 to 38 minutes. Remove from the heat the exact moment the cake springs back lightly when pressed and a toothpick inserted straight into the center of the crumb comes out completely clean.

Place the hot pan on a wire cooling rack and run a thin butter knife carefully around the inside edges to loosen any stuck starches. Let the cake cool in the pan for exactly 5 to 8 minutes; if it sits too long, the hot sugars will harden and glue the nuts permanently to the metal.

Place a flat, heatproof serving plate upside down over the top of the cake pan. Firmly gripping both the plate and the hot pan with oven mitts, flip them over cleanly in one swift movement. Lift the pan straight up, gently peel away the parchment paper circle, and scrape any remaining warm caramel pecans from the pan back onto the top of the cake before slicing.