Preheat and prepare: Turn your oven to 350°F. Grease your 9x13-inch pan really well, then line the bottom with parchment paper for easy removal.
Mix dry ingredients: Whisk together 2 cups flour, 2 teaspoons baking powder, 1 teaspoon baking soda, 2 teaspoons cinnamon, 1 teaspoon nutmeg, ¼ teaspoon ginger, and ½ teaspoon salt in one bowl.
Combine wet ingredients: Beat 4 eggs, 2 cups sugar, 1 cup oil, and 15 ounces pumpkin puree with your mixer until everything looks smooth and well combined.
Create batter: Add your dry ingredients to the wet mixture. Fold gently until just combined. Don't worry about a few small lumps—they're fine!
Bake: Pour batter into your prepared pan and spread evenly across the bottom. Bake for 25-30 minutes until a toothpick poked in the center comes out clean.
Cool completely: Take the pan out and let your bars cool on a wire rack for at least 1 hour. This step is important for frosting!
Make frosting: Beat 8 ounces softened cream cheese and ½ cup softened butter for about 3 minutes until light and fluffy in your mixer bowl.
Add sugar and vanilla: Gradually beat in 4 cups powdered sugar, 1 teaspoon vanilla extract, and a pinch of salt until your frosting looks smooth and creamy.
Frost bars: Spread your cream cheese frosting over the completely cooled bars using a spatula. Make it as smooth or swoopy as you like!
Cut and serve: Cut your bars into 24 squares with a sharp knife. Wipe the blade between cuts for neat edges. ENJOY!!!