Preheat oven to 325ºF. Grease a 9x13 or 11x13 baking dish and set aside.
Prepare the Cake Batter:
Combine softened butter and sugar in a mixing bowl. Using an electric mixer, mix the ingredients until light and fluffy.
Add the eggs and continue mixing for 3-5 minutes until the mixture is light and creamy.
Add the vanilla and mix briefly to incorporate.
Add the flour, baking soda, and baking powder and mix until just combined. Do not over-mix!
Finally, add the sour cream and mix until smooth. Again, do not over-mix!
Pour half the cake batter into the prepared pan and use a rubber spatula to flatten it into an even layer.
Prepare the Pumpkin Layer:
In a bowl, combine all the ingredients for the pumpkin layer and mix with the electric mixer until smooth.
Pour the pumpkin layer over the cake batter.
Prepare the Streusel Topping:
In a bowl, combine all the ingredients for the streusel topping and use a spoon to stir until combined.
Finish Assembling the Coffee Cake:
Pour the remaining cake batter over the entire cake and use a rubber spatula to smooth it out. Don't worry if it looks messy!
Using a tablespoon, drop dollops of the streusel evenly over the coffee cake.
Bake the Coffee Cake:
Transfer to the oven for 45-50 minutes to start. Using a toothpick, test the doneness at the center of the cake. If it hasn't set up, bake an additional 5-7 minutes as needed until a toothpick comes out mostly clean from the center of the cake. Note: The pumpkin layer is quite moist, so the toothpick may have a bit of pumpkin on it!
To Serve:
Allow the cake to cool before slicing. We love our coffee cake served slightly warm! Store for 1-2 days in an airtight container and then in the fridge for 3-4 days longer. Freeze for up to 2-3 months. Enjoy!