Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking sheet pan.
In a large mixing bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt until well combined.
In another bowl, mix the granulated sugar, brown sugar, pumpkin puree, vegetable oil, milk, eggs, and vanilla extract until smooth.
Gradually add the dry ingredients to the wet ingredients, stirring with a rubber spatula until just combined. Avoid overmixing.
Pour the batter into the prepared baking sheet pan and spread it evenly.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes, then transfer it to a cooling rack to cool completely.
For the cream cheese frosting, beat the softened cream cheese and butter together until creamy.
Gradually add the powdered sugar and vanilla extract, beating until fluffy. If the frosting is too thick, add milk one tablespoon at a time until you reach the desired consistency.
Once the cake has cooled completely, spread the cream cheese frosting evenly over the top.
Cut into squares and serve.