Preheat the oven to 350°F.

In the bowl of a food processor, puree the roasted sweet potato (or canned pumpkin), butter, brown sugar, molasses, eggs and milk - 1/2 cup if you're using roasted sweet potato, 1/4 cup if you're using canned pumpkin puree. Pulse until well blended and smooth. (Alternatively, if you're using pumpkin puree you can mix it in a bowl by hand.)

In a small bowl, stir together the flour, baking soda, cinnamon, ginger, nutmeg/allspice/pumpkin pie spice and salt. Add to the food processor and pulse just a few times, just to incorporate wet and dry; alternatively, scrape it into a bowl and stir in the dry ingredients with a spatula. Scrape into a 9"x5" loaf pan that has been sprayed with nonstick spray, and bake for 50-60 minutes, until risen and springy to the touch. Cool in the pan on a wire rack.