Sift all purpose flour and baking soda (optional)
Combine cinnamon, salt, nutmeg, and cloves
Cream butter and sugar in stand mixer with paddle attachment for 3 minutes on medium speed
Add eggs one at a time on low speed until just combined
Scrape sides of bowl to make sure all ingredients get thoroughly combined
Add pumpkin purée, sour cream and vanilla extract in increments and mix until just combined
Add flour, baking soda and spice mixture in increments on low speed, do not overmix
(optional) Gently fold chopped pecans into batter
Pour batter into greased loaf pan, use a spatula to smooth batter evenly in the pan