Pre heat oven to 350 degrees and line the long side of a 9 x 5 loaf pan with parchment paper. The parchment paper should make a sling and hang off the sides of the pan for easy removal.
In a small saucepan, melt butter over medium heat. Alternatively, place butter in a microwave safe bowl and microwave until melted.
For the streusel, in the small bowl, whisk together flour, both sugars, and spices. Using a pastry blender or your fingers, work the butter into the flour mixture until it forms a crumble and holds together. Place in refrigerator until ready to use.
Meanwhile, in a large bowl, whisk together flour, baking soda, baking powder, spices, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat eggs and both sugars on medium speed until pale yellow, about 2 – 3 minutes.
With the mixer on low, slowly add melted butter and mix until evenly combined. Butter should be slightly warm, not hot to the touch. Next, add pumpkin puree and vanilla extract and mix until combined.
With the mixer on low, add flour mixture alternatively with the sour cream, beginning and ending with the flour mixture. Flour mixture should be added in 3 additions and sour cream in 2. Mix until just combined after each addition, being careful not to over mix. Before adding batter to prepared pan, stir one final time with a large spatula. Make sure to scrape the bottom and sides of the bowl to ensure all the flour is incorporated.
Pour batter into prepared loaf pan.
Using your hands or spoon, sprinkle streusel over the batter. Be sure to cover the entire loaf with streusel mixture.
Bake for 45 to 50 minutes until golden brown (mine was ready in 50 minutes) and cake tester inserted into the center comes out clean. The bread should have a dome shape and the streusel should be golden brown. Be careful to not overbake. Allow bread to cool in pan on wire rack for 10 minutes then using the parchment sling, lift bread out of pan and place onto wire rack. Let bread cool completely before slicing.