For the streusel:

In a small bowl, mix together the ingredients for the layering streusel; set aside.  

In a small bowl, mix together the flour, sugars, and cinnamon for the top streusel.  Add the butter and pecans, then use work the butter into the flour mixture until all of the topping is moistened.  Set aside.

For the cake:

 Preheat the oven to 350F / 175C. Line a small loaf pan; set aside.

In a bowl, combine the eggs, 60g of the sour cream, and the vanilla.

In the bowl of an electric mixer, combine the flour, sugar, baking powder, baking soda, and salt for about 30 seconds.

Next, add the butter and remaining sour cream; mix on low until just combined. Turn up the speed of the mixer to medium and mix for an additional 30 seconds.

Slow down the mixer and add the egg mixture in 3 separate additions, beating for 30 seconds and scraping the bowl after each addition to make sure everything is combined. Increase the speed to medium-high and beat for an additional minute.

Put about 1/3 of the batter on the bottom of the prepared pan and spread it evenly. Evenly sprinkle half of the LAYERING (not nuts) streusel on top of the batter. Add another third of the batter on top of the streusel. Sprinkle on the rest of the LAYERING (no nuts) streusel. Top with the remaining batter and sprinkle on the TOP (with nuts) streusel.

Bake for approximately 60 minutes or until a toothpick comes out clean. Remove the pan to a rack, remove the cake from the pan but leave the liner on.  Allow the cake to cool in the liner for 30 minutes before removing.

Re-invert it so that the streusel side is on the top.