Set oven to 350°F (175°C). Grease and flour a 9-inch round cake pan (or a 9x13 pan for thinner slices).
In a bowl, whisk flour, baking powder, baking soda, salt, and spices until combined.
In another bowl, whisk sugars, oil, eggs, pumpkin puree, vanilla, and milk until smooth.
Add dry ingredients to wet, mixing gently until just combined. Fold in optional add-ins like pepitas, nuts, or chocolate chips.
Pour batter into prepared pan. Bake 35–40 minutes, or until a toothpick inserted in the center comes out clean.
Allow to cool before slicing. Serve plain, dusted with powdered sugar, or topped with cream cheese frosting.