Prepare mini bundt pans by spraying them lightly with pan spray. Preheat oven to 325°.

To make cakes: In a small bowl combine sweet potato purée, oil or browned butter, milk, vinegar and vanilla extract. Whisk until lump free and set aside.

In a large bowl mix together flour, baking soda, spices, salt and sugar. Add mix-ins if using. Create a well in the middle of the dry ingredients and pour in sweet potato mixture. With a rubber spatula or wooden spoon, mix until batter is smooth and completely combined. Fold through the sides and bottom of the batter a few times to make sure all ingredients are thoroughly incorporated. Divide batter between mini bundt pans, about 2/3 of the way full.

To make salted cinnamon sugar: Toss together sugar, cinnamon and salt. Sprinkle each cake liberally with salted cinnamon sugar. Bake 18 to 24 minutes, or until a toothpick inserted into each cake comes out clean. Unmold and cool.

Garnish cakes simply with glaze or powdered sugar, or decadently with cream cheese icing or Italian meringue.

*To make brown butter: Melt 10 tablespoons unsalted butter in small saucepan over medium-high heat, stirring constantly. Allow butter to turn brown it usually takes about 10 minutes. Remove from heat and slowly pour browned butter into a small bowl, allowing the solids to separate from the liquids. Use the residual liquid in the recipe.