Preheat the oven to 350°F. Spray a 9×13-inch baking dish with nonstick spray and set aside.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, and spices, and set aside.
2 cups all-purpose flour, 1 teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon salt, 1 ½ teaspoons ground cinnamon, ½ teaspoon ground nutmeg, 1/8 teaspoon ground cloves, ¼ teaspoon ground ginger
In a large bowl, whisk together the wet ingredients (pumpkin, egg, melted butter, sour cream and vanilla extract). Add the brown sugar and granulated sugar and mix well.
1 cup pumpkin puree, 1 egg, ½ cup unsalted butter, ½ cup sour cream, 2 teaspoons vanilla extract, ½ cup brown sugar, ½ cup granulated sugar
Add the dry ingredients and whisk just until the ingredients are incorporated, and no flour is visible. The batter will be thick. Pour the batter into the 9×13-inch pan and spread evenly.
Add the remaining flour, brown sugar, melted butter, and cinnamon to a small bowl. Use a fork to mix the ingredients until small crumbs form. Sprinkle the streusel over the cake batter and press the crumbs gently into the batter.
⅔ cup all-purpose flour, 1 cup brown sugar, ¼ cup unsalted butter, 1 ½ teaspoons ground cinnamon
Bake for 32 to 37 minutes, or until a toothpick inserted comes out clean.
Serve with whipped cream, if desired.