Preheat the oven to 350°F and prepare an 8x8 inch baking dish with parchment.
In a medium-sized bowl, make the crumb topping. Add in the cinnamon, nutmeg, all-spice, flour, and brown sugar. Mix until combined. Slowly add in the melted butter. Mix until pea-sized crumbs begin to form. Feel free to adjust the spices to your liking. Set aside when done.
For the cake, use a medium-sized bowl to combine the dry ingredients. Mix together the flour, baking powder, baking soda, and salt. Set aside.
Using a hand mixer or a stand mixer with a paddle attachment, beat the butter until creamy, about 1 minute. Next, add in the sugar and beat together until combined, about 2-3 minutes. Make sure to scrape down the bowl to get everything in the mix. Continue beating the butter mixture and add in the eggs, one at a time. Make sure they are fully combined after each addition. Once the eggs are combined, add in the vanilla and sour cream.
Keep the mixture on a low speed and slowly add in the dry ingredients. Mix the ingredients until just combined. You don't want to overmix this batter so it is okay if it looks a little thick. Just make sure everything is incorporated.
In a small bowl, take about 1/4 cup of the batter and mix it with 3-4 tbsp of pumpkin. Stir until combined. Set aside.
Pour the batter into the prepared dish. Add the pumpkin layer on top. You can either swirl it in or just let it sit on top as an additional layer. Top the pumpkin layer with the crumbs. Make sure to use all the crumbs and spread them out evenly.
Place in the middle rack of the oven and bake for 44-55 minutes, or until the edges are golden brown. Let the cake cool completely before cutting.
The cake will last about a week stored in an air-tight container.
*If you are looking for a more pumpkin flavor for the cake, you can definitely add in more pumpkin to the batter layer.