Preheat oven to 350°F (175°C). Grease and line a 9×13 pan.
In a bowl, whisk flour, baking powder, baking soda, pumpkin spice, and salt.
In another bowl, beat pumpkin puree, sugars, oil, and eggs until smooth. Add milk.
Mix in dry ingredients until just combined. Pour into pan and bake 30–35 minutes, or until a toothpick comes out clean.
While cooling, beat cream cheese and butter until creamy. Gradually add powdered sugar and vanilla.
Spread frosting over cooled cake. Sprinkle with extra cinnamon or crushed pecans if you want it fancy.