Preheat oven to 350 degrees Fahrenheit and prepare a 9x5-inch loaf pan by spraying it with non-stick spray or lightly greasing it.
In a medium-sized bowl, whisk together flour, baking soda, baking powder, spices, and salt. Set aside.
In a large bowl, add the egg, pumpkin purée, brown sugar, granulated sugar, vegetable oil, sour cream, and vanilla. Mix to combine.
Add the dry ingredients to the wet and mix until just combined. Do not overmix.
Turn the batter out into the prepared pan and use a spatula to evenly spread it.
Bake for 50 minutes, or until a toothpick inserted into the center comes out clean. Keep an eye out for the top browning too quickly. Tent the loaf pan with foil mid-way through baking if needed. (If using a dark coated pan, start checking for doneness at the 40 minute mark)
Allow the bread to cool completely.
While the bread cools, make the cream cheese frosting.