Preheat your oven to 350 degrees F and grease a 9x13 inch cake pan.
In a large bowl, whisk together the dry ingredients for the streusel and then mix in melted butter.
In another bowl, combine the dry ingredients for the cake and add softened butter, mixing until crumbly.
Add half of the pumpkin puree to the flour mixture and blend until it forms a ball.
In a separate bowl, whisk together the remaining pumpkin, eggs, oil, and vanilla.
Combine the wet and dry mixtures, mixing in three additions until light and fluffy.
Layer the batter and streusel in the prepared pan, finishing with a layer of streusel on top.