Sweet Potato Pound Cake with Cinnamon Sauce

Cake
1 1/2 cups cake flour
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 teaspoon ground cinnamon
1/2 teaspoon ground nutmeg
1/2 cup unsalted butter (at room temperature)
1/2 cup sour cream (at room temperature)
1 1/4 cups plus 2 tablespoons granulated sugar
3 eggs (at room temperature)
1 (8 ounce) sweet potato, baked, peeled and pur