Preheat the oven to 350°F and lightly grease a 10-inch skillet.
In a large mixing bowl, whisk together the flour, baking soda, cinnamon, clove, ginger, nutmeg, salt, pecans, and orange zest until well combined.
In a separate bowl, whisk together the eggs, vanilla, sugar, brown sugar, oil, and sweet potato until well blended. Pour the wet ingredients into the dry ingredients, and stir until well blended. The batter will be thick.
Evenly spread the cake batter in the skillet then bake uncovered for 30 minutes or until browned and an inserted knife comes out clean.
Serve warm. Will keep covered for 5 days.
If you wish to bake this in a loaf pan, I used a 9x5 and baked it for an hour and it was perfect. Another reader said hers was not done after an hour, however, so you may test it with an inserted knife after that time and bake longer if needed. No additional leavenings are needed, but it's important to use the brown sugar as that activates the baking soda. If you want an extra-fluffy loaf, you could also add 1/2 teaspoon of baking powder. As always with leavenings, make sure they're fresh so they'll activate.