Preheat the oven to 350ºF (180ºC). Lightly spray an 8-inch (20-cm) square baking dish with baking spray and line it with parchment paper. Set aside.
In a medium mixing bowl, whisk together the flour, pumpkin pie spice, baking powder, baking soda, and salt. Set aside.
1 ½ cups all-purpose flour, 1 ½ teaspoons pumpkin pie spice, 1 teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
In a large mixing bowl, mix the softened butter, both sugars, and the eggs until creamy, about 1 minute. Add the pumpkin purée and vanilla and mix well to combine.
½ cup salted butter, 1 cup granulated sugar, ½ cup brown sugar, 2 large eggs, 1 cup pumpkin purée, 1 ½ teaspoons vanilla extract
Add the flour mixture to the wet ingredients. Switch to a spatula or wooden spoon. Fold the cake batter together gently until no flour remains (a few streaks of flour are okay). Spoon the batter into the prepared baking dish and use an offset spatula or butter knife to smooth the top.
In another smaller bowl, make the streusel. Stir together the pecans, sugar, flour, butter, and cinnamon. Scatter the streusel crumbs evenly over the top of the cake.
½ cup raw pecans, ¼ cup brown sugar, 2 tablespoons flour, 1 teaspoon cinnamon, 1 tablespoon softened butter
Cover the baking dish with foil and bake for 30 minutes. Remove the foil and bake 30 minutes more. Transfer the coffee cake to a wire rack to cool completely before slicing and serving with whipped cream.
Notes
The streusel is optional.
Mixing in the pumpkin purée with the butter, sugar, and eggs may look slightly curdled. This is normal.