Preheat your oven to 350°F (175°C).

Grease a 9x5-inch loaf pan with non-stick spray or a little vegetable oil.

In a large mixing bowl, combine the pumpkin puree, granulated sugar, brown sugar, vegetable oil, and eggs. Mix well until fully incorporated and smooth.

Stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, ground cinnamon, ground nutmeg, salt, and cream of tartar.

Gradually add the dry ingredients to the wet mixture. Stir gently until just combined.

In a small bowl, mix together the 1/4 cup granulated sugar and 1 teaspoon of ground cinnamon.

Pour half of the batter into the prepared loaf pan. Sprinkle generously with the cinnamon-sugar mixture. Top with the remaining batter and finish with another sprinkle of cinnamon-sugar.

Place the loaf pan in the preheated oven and bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.

Allow the bread to cool in the pan for a few minutes before transferring it to a wire rack to cool completely. Once cooled, slice and serve.