Preheat the oven to 425°F. Spray donut pans with nonstick cooking spray.
Mix together the all-purpose flour, baking soda, salt and chai spice together in a bowl. Set aside.
With an electric mixer, cream together butter and sugar, until light and fluffy. Add in egg and vanilla, whisk until combined. Add in mashed banana and sour cream, whisk until combined. At this point, the mixture will look like its separating but once you add the dry ingredients it will combine into a smooth batter.
Start adding the flour mixture to the wet mixture. Add a little at a time until the dry mixture has been incorporated.
Spoon the batter into a donut pan. Bake the donuts for 8-10 minutes or until a toothpick inserted comes out clean. Let the donuts cool in the pan for 5 minutes before turning them out onto a cooling rack.
Coat with Chai Spiced Sugar
Melt the ghee or butter in a small microwaveable bowl or a small saucepan. Remove from heat and allow to cool to the touch slightly. (Do not wait too long or the ghee will solidify again!)
Combine all of the spices for the chai spiced sugar coating in a small bowl, mix to evenly distribute the spices with the sugar.
Dip each donut, face down in the ghee and then the spiced sugar. Place on the cooling rack to let set. The sugar coating will set within 10 minutes.