Step 1
Preheat the oven to 350 degrees F (175 degrees C). Place the oven rack in the center of the oven. Line a baking sheet with aluminum foil.
Step 2
Combine softened butter and brown sugar in a medium-sized bowl; stir until well combined. Add maple syrup bourbon and salt. Stir in pecans and mix until well coated. Set topping aside.
Step 3
Butter a 10-inch tube pan. Line the bottom of the pan with parchment paper; butter the parchment paper and lightly dust with flour. Evenly spread topping into the bottom of the tube pan and set aside.
Step 4
Whisk flour cinnamon baking soda and salt together in a bowl.
Step 5
Mix softened butter sugar and brown sugar together in the bowl of a stand mixer. Mix on medium speed until well combined 3 to 4 minutes; the mixture will be a bit grainy in appearance. Add eggs 1 at a time mixing on medium speed after each addition. Use a spatula to scrape down the bowl as needed. Add sweet potatoes and bourbon and mix on medium speed until well combined scraping the bowl as needed.
Step 6
Combine buttermilk and sour cream in a separate bowl.
Step 7
Add 1/2 the flour mixture to the mixing bowl and mix on low speed until well blended. Add 1/2 the buttermilk mixture and beat on low until blended scraping the bowl as needed. Add remaining flour to the mixing bowl and continue mixing. Add remaining buttermilk mixture and continue beating on low speed until batter is thick and smooth.
Step 8
Pour batter into the prepared tube pan and place pan on the prepared baking sheet.
Step 9
Bake in the preheated oven until a wooden skewer inserted in the center of the cake comes out clean 65 to 75 minutes. Remove cake from the oven and leave in the pan.
Step 9
Prepare glaze by combining maple syrup melted butter and bourbon in a bowl. Use a wooden skewer to poke holes in the warm cake in the pan. Spoon 1/2 the glaze over the bottom of the cake.