Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper for easy removal.
In a large bowl, whisk together the flour, sugar, baking powder, spices, and salt until well combined.
Create a well in the center of your dry ingredients, and add the pumpkin puree, eggs, and vegetable oil. Mix until just combined—don’t overmix.
Gently fold in any chopped nuts or other additions you desire.
In a small bowl, combine 1/2 cup of flour, 1/2 cup of brown sugar, and 1/2 teaspoon of cinnamon. Cut in 1/4 cup of cold butter until it resembles coarse crumbs.
Pour the batter into your prepared pan, spreading it evenly. Sprinkle the topping mix over the batter and bake for 30–35 minutes, or until a toothpick comes out clean.
Let the cake cool in the pan for about 10 minutes, then transfer it to a wire rack. Slice, serve, and enjoy your cozy treat!