Preheat oven to 400ºF. On a large baking sheet, toss the cubed persimmons with the tablespoon of brown sugar until they are well-coated. Roast the persimmons in the preheated oven until they are tender and beginning to brown, about 15 minutes. Remove the persimmons from the oven and turn the temperature down to 350ºF. Using a food processor, blender, or stick blender, puree the persimmons until they form a thick puree. Add a tablespoon or two of water, as needed, to make a smooth puree without a lot of chunks in it. There should be about 1 cup of persimmon puree when you are done.

In a large mixing bowl, whisk together the flour, salt, baking soda, nutmeg, and cinnamon. In a separate bowl or measuring cup, whisk together the sugar, melted butter, eggs, vanilla, and buttermilk. Pour the wet ingredients into the dry ingredients and use a rubber spatula to fold them together, just until the dry ingredients are moistened. Add the pecans and fold them in gently using the same spatula.

Butter a 9 X 5 inch loaf pan, line it with a piece of parchment and then butter the parchment also. Pour the batter into the prepared pan, smoothing it on the top with a spatula. Bake in the preheated oven for about 1 hour, or until a toothpick inserted in the center comes out clean. Cool the loaf in the pan for about 10 minutes before lifting it from the pan with the edges of the parchment and finish cooling on a cooling rack.