• Preheat the oven to 350 degrees.
• Prepare your baking tins by thoroughly greasing them, set aside.

To make the cake

• Using a hand mixer or a stand mixer fitted with the paddle attachment, mix oil and sugar.
• Add pumpkin puree and sour cream. Mix well.
• Add eggs and vanilla extract. Mix well.
• In a separate bowl, whisk together dry ingredients (flour, salt, baking powder, baking soda, pumpkin spice).
• In 3-4 portions, add the dry ingredients to the wet ingredients, mixing well after each addition.
• Set mixture aside while you prepare the filling and topping.

To make the filling

• Whisk together flour, cinnamon and brown sugar.
• Cut in the softened butter with a fork or your fingers. Work until mixture is crumbly.
• Spread half of the cake batter throughout the greased baking tin, then sprinkle all of the filling over it.
• Top with the remaining cake batter and spread evenly, completely covering all of the filling with batter.

To make the topping

• Using the same bowl that was used for the filling (if desired, since ingredients were the same), whisk together flour, brown sugar and cinnamon.
• Cut in softened butter using a fork or your fingers. Pinch mixture together to form some larger pieces (to resemble a streusel topping) and sprinkle over the top of the batter to generously cover the entire pan.
• Bake for 35-45 minutes (baking time will depend on your pan), or until edges just begin to brown.
• Remove from oven and let cool to room temperature before removing the cakes from the pan. Use a butter knife to loosen the edges if needed.