Preheat the oven to 375°F and line a 12-cup muffin pan with paper liners.

In a large bowl, whisk together flour, cocoa powder, baking soda and salt.

In a medium bowl, whisk together buttermilk and sweet potato purée.

With an electric mixer, cream together butter and sugar on high speed until light and fluffy, about 3 minutes.

Add eggs and vanilla.

Reduce speed to low and add flour mixture in batches, alternating with buttermilk mixture and ending with flour mixture.

Spoon batter into prepared muffin cups.

Bake until a toothpick inserted into the center of a cupcake comes out clean, about 25 minutes.

Let cool in the pan 10 minutes, then transfer to a wire rack to cool completely.

To make the glaze, heat butter, milk and cocoa in a small saucepan over medium heat, stirring just until butter is melted and cocoa is dissolved.

Transfer to a mixing bowl and gradually whisk in confectioners’ sugar.

Let stand 15 minutes for glaze to thicken to spreading consistency.

Spread over cupcakes and top with pecans.

*Look for canned sweet potato purée or make you own by baking a small sweet potato in a 400°F oven until very tender, about 40 minutes, then mashing or blending the flesh until smooth.