Ensure a rack is placed in the center of the oven and preheat to 350F.

Use 1 Tbs. of unsalted butter to generously grease a 10-inch tube pan with a removable bottom.

In a medium bowl, combine all ingredients except melted butter until well combined. Add melted butter and stir with a fork or small spatula until evenly moistened and crumbly. Set aside.

Combine all ingredients in the bowl of a food processor. Pulse about 6 times, until pecans are coarsely chopped and the ingredients are thoroughly combined.

With a stand mixer fitted with the paddle attachment, beat butter on medium-high speed until smooth and creamy, 1-2 minutes. Reduce speed to medium-low and slowly add sugar. Scrape down sides of the bowl and with the mixer running on low speed, add eggs - one at a time - and vanilla.

Again, scrape down sides of the bowl. add half of the cake flour, baking powder, baking soda, and salt. Beat on low until combined. With the mixer still running, add sour cream. When sour cream is incorporated, add remaining cake flour. If necessary, scrape down sides of the bowl again and beat a little longer to ensure all ingredients are mixed in.

Pour about 2 cups of the cake batter into the greased tube pan, smoothing out with the end of a spatula or butter knife. Sprinkle about 1/2 c. of the toasted pecan filling over the better. Repeat twice - so that you have 3 layers of batter and 3 layers of filling. Top with remaining cake batter.

Insert a butter knife into cake, about 1-inch from the edge of the pan. Insert almost all of the way to the bottom of the pan. Keeping knife in, drag the knife around the pan two times. Remove and if needed, smooth the top again.

Finally, with clean hands gently take small handfuls of the streusel topping and press together slightly. Crumble over top of the cake, repeating until topping is gone and batter is evenly covered with streusel topping.

Bake in preheated oven for 70-75 minutes, until the top of the cake if golden brown and the sides are beginning to pull away from the sides of the pan. A toothpick of skewer inserted into the center of the cake should come out clean.

Remove from oven and allow to cool on a wire rack for 1 hour.

To remove cake from pan, gently lift up the center tube while pushing the removable bottom upward with the opposite hand (if cake is stuck, run a butter knife around edges of pan). To prevent crumble topping from falling off, place a piece of foil on top of cake, punching a whole in the middle to go through tube. Fit foil over cake and invert onto a plate (foil will now be on the bottom). Remove tube. Invert cake onto a cake plate and remove foil.

Allow to cool before covering tightly with plastic wrap or a cake dome. Cake will keep at room temperature for up to 5 days, or can be frozen for up to 3 months.