Preheat oven to 350 and grease 1 9x5 inch loaf pan.
Melt butter and mix with sugar in large bowl.
Add eggs and vanilla and mix until incorporated.
In a separate bowl, mix flour, salt, baking soda, cinnamon, nutmeg, cloves, and ginger.
Add dry ingredients to wet and mix thoroughly.
Add mashed sweet potato and sour cream/plain yogurt until just incorporated.
Pour into greased pan, and bake for 60 minutes or until toothpick comes out clean. Cool loaf in pan for 10 minutes, then remove to a wire rack to finish cooling.