This is one of our favorite vegetable cakes. It is tender, faintly spicy, and has a light orange crumb. Plus, it’s large enough to feed a crowd—perfect for holiday parties or whenever a festive “show off” cake is in order.
For sweet potatoes: Preheat the oven to 400°F. Pierce each potato twice with a paring knife and place the potatoes on a foil-lined baking sheet. Bake for 45 to 55 minutes, until the centers are soft. (Check with a paring knife or fork.) Carefully slice the potatoes in half to let off steam. When they are cool enough to handle, scoop out 2 cups of flesh and place it in a food processor. Add the buttermilk and process until smooth. Refrigerate to cool. (Refrigerate any unused potato flesh for another use.)
Adjust your oven rack to one setting below the center position, with no racks above it. Preheat oven to 350°F.
Butter a 10-inch Bundt pan. Sprinkle nuts evenly around bottom of pan, then sprinkle with 2 tablespoons of brown sugar.
In a bowl, sift together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Using an electric mixer (preferably a large stand model) on medium, cream the butter, then gradually beat in the sugar and remaining 1 cup of brown sugar. Add eggs, one at a time, beating well after each addition. Add the vanilla and orange zest and beat to blend. Add the sweet potato mixture and beat on low until evenly blended. Add flour mixture, about a third at a time, mixing well after each addition.
Pour batter into prepared pan, spreading it evenly. Bake for 60 to 70 minutes, until a tester (such as a thin wooden skewer) inserted into the center comes out clean. Cool in the pan for 15 minutes. Invert the cake onto a large platter. Cool for at least 30 minutes more before slicing.
An Easy Fix for a Dark Finish
Sweet cakes and breads sometimes develop a dark top crust. This browning is rarely more than a fraction of an inch deep, so it is unlikely to affect the flavor. If the color bothers you, dust the top with confectioners’ sugar.