Step 1

Place a rack in middle of oven; preheat to 350°. Melt 2 Tbsp. butter in a medium cast-iron skillet over medium heat, swirling butter to coat skillet; set aside.

Step 2

Beat brown sugar, oil, and remaining 4 Tbsp. butter in the bowl of a stand mixer fitted with the paddle attachment on medium-low speed until combined, about 2 minutes. Add egg and beat until mixture is pale brown and fluffy, about 1 minute. Add lime zest, lime juice, orange zest, ginger, cinnamon, nutmeg, and salt and beat to combine, about 1 minute (mixture may look curdled, which is fine). Reduce speed to low and add sweet potatoes, coconut milk, rum, bitters, vanilla, and ½ cup coconut flakes. Mix until well combined, about 2 minutes. Scrape batter into reserved skillet and top with remaining ½ cup coconut flakes.

Step 3

Bake pone until golden brown, bubbling around the edges, and the center doesn’t jiggle when you gently shake the pan, 50–60 minutes. Let pone cool in skillet 10 minutes.

Step 4

Using a large spoon, scoop pone onto small plates and serve with vanilla ice cream if desired.