Peel 1 to 2 medium sweet potatoes, chop into small even chunks, and boil in a medium pot of cold water for 10 to 15 minutes until fork-tender. Drain completely and mash until smooth. Measure out 1 cup of mash and set aside to cool slightly.
Place an oven rack in the center position and preheat oven to 350°F (175°C). Grease a 9x5 inch loaf pan with vegetable oil, or line with parchment paper leaving overhang on the long sides for easy removal.
In a large mixing bowl, whisk together 1 ¾ cups all-purpose flour, ½ teaspoon baking soda, ½ teaspoon sea salt, and 1 teaspoon ground cinnamon for about 30 seconds until evenly combined with no lumps.
In a second mixing bowl, combine ½ cup brown sugar, ¼ cup granulated sugar, ½ cup vegetable oil, 2 large eggs, 1 teaspoon vanilla extract, and 1 cup mashed sweet potatoes. Whisk until smooth, glossy, and fully combined with no large streaks of egg.
Slowly pour the wet mixture into the bowl of dry ingredients. Switch to a spatula and fold gently, scraping the bottom and sides, until just combined with no dry flour visible. Do not overmix.
Scrape the batter into the prepared loaf pan and spread evenly into the corners. Smooth the top and tap the pan lightly on the counter two or three times to release any large air bubbles.
Bake in the center of the preheated oven for 55 to 65 minutes, until a toothpick inserted into the center comes out clean or with just a few moist crumbs. If the top browns too quickly, tent loosely with foil for the last 10 minutes.
Let the bread cool in the pan for 10 minutes, then run a thin knife around the edges and transfer to a wire rack. Cool completely before slicing into 12 even slices with a serrated knife. Serve with honey or whipped butter.