Preheat oven to 350°F (175°C). Generously grease a 10 to 12-cup fluted bundt pan with baking spray with flour (or melted butter dusted thoroughly with flour), ensuring all fluted crevices and center tube are well coated.

In a medium bowl, whisk together melted butter (1/2 cup), dark brown sugar (3/4 cup), heavy cream (3 tbsp), and fine sea salt until smooth and glossy.

Pour the caramel mixture evenly into the bottom of the prepared bundt pan. Arrange the toasted pecan halves neatly along the fluted ridges, facing down, and scatter the remaining chopped pecans evenly over the caramel layer.

In a large bowl, whisk together flour, baking powder, baking soda, ground cinnamon, nutmeg, and sea salt. Set aside.

In a stand mixer fitted with the paddle attachment (or using an electric hand mixer), beat softened butter, granulated sugar, and brown sugar on medium speed for 3 to 4 minutes until light, fluffy, and pale in color.

Add eggs one at a time, beating well after each addition. Beat in the pure vanilla extract.

In a small bowl, whisk together sour cream and whole milk until smooth.

With the mixer on low speed, alternate adding the dry flour mixture in three additions and the sour cream milk mixture in two additions, beginning and ending with the flour mixture. Mix just until combined; do not overmix.

Gently dollop the thick cake batter over the pecan caramel layer in the bundt pan. Use an offset spatula to smooth the top into an even layer.

Bake at 350°F (175°C) for 48 to 52 minutes, or until a wooden skewer inserted deep into the center of the cake comes out clean with just a few moist crumbs.

Remove from the oven and place the pan on a wire cooling rack. Let cool for EXACTLY 10 minutes (set a timer!). If you invert too early, the cake may collapse; if you wait too long, the caramel will harden and stick to the pan.

Place a rimmed serving platter or cake stand upside down over the bundt pan. Wearing oven mitts, firmly hold the pan and platter together and invert in one confident, smooth motion. Let the pan rest upside down for 1 to 2 minutes so gravity releases all the caramel and pecans, then gently lift the pan off.

If any pecans remain stuck in the pan, simply scoop them out with a small silicone spatula and press them gently back onto the cake while warm. Let cool for 15 minutes before slicing. Serve warm with vanilla bean ice cream!