• Preheat oven to 325°F. Line an 8×8-inch baking dish with aluminum foil, including up the sides, leaving extra hanging over the edges. Spray with nonstick cooking spray. Set aside.

Topping

• To a medium bowl, add butter, sugars, cinnamon, and salt. Stir to combine. Add the flour and stir until the mixture is completely combined. Be careful not to over mix or it can become like a paste.

Cake

• In the bowl of a stand mixer fitted with paddle attachment on low speed, add flour, sugar, pumpkin pie spice, salt, and baking soda. Mix to combine.
• Add pieces of butter, one at a time, mixing until there are no visible butter pieces and it has a very fine crumb, about 1 minute.
• Add the pumpkin, buttermilk, egg, yolk, and vanilla. Beat the mixture on medium speed until it becomes light and fluffy, about 1 minute, scraping the sides of the bowl as needed.
• Pour the batter into the prepared baking dish, spreading it evenly with a spatula.
• Using your hands or a fork, break the prepared crumb topping into small pieces. Evenly distribute it over the cake batter.
• Bake for 38-40 minutes, or until the crumb topping is golden and a toothpick inserted into the center of the cake comes out clean.
• Let the cake cool slightly in the pan on a wire rack. Then, using the extra foil, carefully lift the cake out of the pan to finish cooling on the rack.
• Before serving, dust the cake with confectioners' sugar.