Preheat oven to 350°F. Grease or spray with non-stick cooking spray a 9 x 5 inch loaf pan.
In a large bowl, with the mixer set on medium, cream the butter and sugar until light and fluffy, about 3-5 minutes. Add eggs, one at a time, beating well after each addition. Add vanilla, cinnamon, orange peel, sour cream and pumpkin puree. Beat on low speed to combine.
In medium bowl, whisk together flour, baking soda and salt.
Add to the pumpkin mixture, beating on low to moisten then medium speed for one minute. Scrape down bowl with spatula as needed.
Spread into prepared pan, smoothing the top. Sprinkle with roasted pumpkin seeds if using. Bake on center rack of oven for 1 hour to 1 hour and 15 minutes, or until toothpick inserted in center comes out clean.
Allow to cool for 10 minutes on a wire rack. Remove from the pan and cool completely on the wire rack before slicing.