Preheat the oven to 325°F with a rack in the center. Thoroughly coat a 12-cup Bundt pan with baking spray containing flour, covering all grooves and the center tube.
Whisk together the cake’s all-purpose flour, baking powder, baking soda, salt, cinnamon, nutmeg, and allspice. In another bowl, stir together the apple butter and sour cream.
Beat the softened cake butter with the granulated sugar and cake brown sugar on medium speed for 4–5 minutes until lighter and fluffy. Scrape the bowl as needed.
Beat in the eggs one at a time, mixing just until each is incorporated. Scrape the bowl, then mix in the cake vanilla.
With the mixer on low, add the dry ingredients in three additions, alternating with the apple butter mixture in two additions. Begin and end with dry ingredients. Mix just until combined, then finish folding by hand.
Mix the swirl brown sugar, cinnamon, and flour. Spoon half of the cake batter into the prepared pan, sprinkle the swirl evenly over it, then cover with the remaining batter. Run a butter knife through the batter in a few gentle curves, without touching the pan. Do not fill the pan more than three-quarters full; bake any excess separately.
Bake at 325°F for 75–90 minutes, beginning checks at 70 minutes. A long skewer inserted into the cake should come out clean or with a few moist crumbs and no wet batter. Loosely tent with foil if the top browns before the center is done.
Let the cake rest in its pan on a wire rack for 15–20 minutes. Using oven mitts, carefully invert onto the rack and lift away the pan. Cool completely before glazing, allowing about 2 hours after unmolding or longer as needed.
Once the cake is cool, combine the topping brown sugar, butter, cream, and salt in a saucepan over medium heat. Stir until the butter melts and sugar dissolves. Bring to a gentle boil, reduce the heat, and simmer 3–4 minutes, stirring frequently. Remove from the heat and stir in the topping vanilla. Cool for 15–20 minutes, until thickened but pourable.
Spoon the caramel over the cooled cake. Finish with toasted chopped pecans if desired. Reserve a little sauce for individual slices.