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1
Preheat oven to 325 degrees F (165 degrees C). Grease an 8-inch baking pan.
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2
Whisk flour, pumpkin pie spice, 1 teaspoon salt, and 1 teaspoon cinnamon together in a bowl.
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3
Combine milk, pumpkin, and vanilla extract in a bowl.
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4
Place egg yolks, white sugar, brown sugar, and water in the bowl of a stand mixer. Beat on high speed until creamy. Reduce speed to low; add butter. Increase speed to medium; beat until light and fluffy. Reduce speed to low and add flour mixture in 3 batches, blending thoroughly after each addition and scraping down the sides of the bowl. Stir milk-pumpkin mixture slowly into the mixture until just combined; transfer to a separate bowl.
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5
Clean and dry out the bowl and beaters. Beat egg whites and cream of tartar on high speed until stiff peaks form. Fold 3/4 of the egg white mixture into the pumpkin mixture using a spatula; pour into the remaining egg whites, folding mixture in slowly until batter is smooth but still light and fluffy. Pour batter into the prepared pan.
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6
Bake in the preheated oven until edges are set and center still jiggles slightly, about 50 minutes. Let cool completely, at least 30 minutes.
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7
Beat heavy cream, maple syrup, 1/2 teaspoon cinnamon, and 1 pinch salt together in a bowl using an electric mixer until soft peaks form. Spread over cooled cake.
