Preheat & Prepare Pan: Preheat your oven to 350°F (175°C). Lightly grease a standard 10x15-inch jelly roll sheet pan (or 9x13-inch baking pan for thicker bars) with butter and line the bottom with parchment paper, leaving an overhang for effortless lifting.

Whisk Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, ground cinnamon, pumpkin pie spice, and fine sea salt until thoroughly blended and free of clumps.

Beat Wet Ingredients: In a large mixing bowl (or stand mixer bowl), beat the 4 eggs, granulated sugar, packed brown sugar, oil, pure pumpkin puree, and vanilla extract on medium speed for 2 minutes until smooth, glossy, and emulsified.

Combine Batter: Pour the dry flour mixture into the wet pumpkin mixture. Fold gently with a silicone spatula just until incorporated and no dry flour streaks remain. Do not overmix.

Spread & Bake: Pour the batter into the prepared sheet pan and spread it evenly to the corners with an offset spatula. Bake at 350°F (175°C) for 23 to 26 minutes (or 28-32 minutes if using a 9x13 pan), until a toothpick inserted into the center emerges clean and the top springs back when lightly pressed.

Cool Completely: Transfer the pan to a wire cooling rack and allow the pumpkin cake to cool completely to room temperature (about 45-60 minutes). Never frost a warm cake, or the cream cheese will melt into liquid!

Whip Cream Cheese Frosting: In a large bowl, beat the softened cream cheese and butter with an electric hand mixer on high speed for 3 minutes until pale, fluffy, and lump-free. Gradually add the powdered sugar 1 cup at a time on low speed, then add the vanilla and pinch of salt. Beat on medium-high speed for 2 full minutes until ultra-creamy and billowy.

Frost, Dust & Slice: Spread the frosting generously across the cooled cake using an offset spatula, creating rustic decorative swirls. Dust lightly with ground cinnamon. Chill in the refrigerator for 20 minutes for clean bakery slices, then cut into 24 squares and enjoy!