Light your campfire or preheat your camp stove. For a Dutch oven, you want a steady bed of coals—about 8-10 briquettes underneath and 14-16 on top for a 12-inch oven.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt. Make sure there are no lumps—cocoa loves to hide them.

Add the warm water, oil, vinegar, and vanilla. Stir with a wooden spoon just until smooth. Do not overmix; a few streaks are fine. The batter will be thin—that's the secret to a moist, melt-in-your-mouth crumb.

Pour the batter into a greased 12-inch Dutch oven (or a greased 9-inch round cake pan). For easy cleanup, line the bottom with a round of parchment paper.

Cover and place the Dutch oven over the coals. Use a lid lifter to carefully arrange the top coals. Bake for 30-35 minutes. Rotate the oven and lid halfway through for even baking—this is the trick that prevents a burnt edge and a raw center.

Test for doneness with a skewer or clean twig. Let the cake cool in the oven for 10 minutes, then lift it out using the parchment paper. Serve warm or at room temperature.