Pumpkin Swirl Cake

Pumpkins speak of fall, and the autumn months are the best time to make this cake. Sage pairs with pumpkin in savory dishes. The soup�on of sage in this cake gives it a different twist.
Yield: 1 Cake, 10 Servings
1 small pumpkin, either sugar pumpkin or rouge vif d'�tampes
Soft butter for the pan
2 cups (10 ounces) unbleached all-purpose flour
1 1/2 teaspoons baking powder
1/4 teaspoon fine sea salt
1 teaspoon ground cinnamon
1/2 teaspoon grated nutmeg
1/4 teaspoon ground cloves
15 tablespoons (7 ounces) unsalted butter, at room temperature
1 1/2 cups (10 1/2 ounces) granulated sugar
3 large eggs, at room temperature
1 teaspoon pure vanilla extract, preferably Madagascar Bourbon
1/2 cup buttermilk, at room temperature
1 teaspoon finely chopped fresh sage, about 5 leaves (don't use dry sage)
Cook the pumpkin:
The pumpkin can be cooked a few days ahead.
Preheat the oven to 375 F.
Line a large baking pan with parchment paper.
Cut the pumpkin into halves. Place the pieces on the baking pan, cut side down. Bake in the oven until a skewer pierces them easily, about 30 minutes.
Cool the pumpkin halves. Scrape out the seeds and discard them. Scrape the flesh out of the rinds. Pur�e the flesh in a food processor. You will need 3/4 cup of pur�e for this recipe. Save the rest for another use. (It makes great soup.)
Make the cake:
Preheat the oven to 350 F
Generously butter a 2-quart Bundt pan.
Sift the flour, baking powder, salt, cinnamon, nutmeg, and cloves together.
Put the 15 tablespoons of butter in the bowl of a heavy-duty mixer. Beat it with the paddle attachment at medium speed until it is creamy and smooth. With the mixer on low, add the sugar in a steady stream. Beat the butter and sugar on medium speed until the mixture is lighter in color and fluffy.
In a separate bowl, beat the eggs together with a fork. With the mixer running, dribble the eggs into the butter and sugar.
Add the vanilla to the buttermilk.
Alternately add the dry ingredients and the buttermilk to the mixer bowl, starting and ending with the dry ingredients. Stop and scrape down the sides of the bowl when necessary.
Stir the sage into the pumpkin pur�e. Add about 1 cup of the batter to the pumpkin pur�e and fold the two together. Now fold the pumpkin mixture into the rest of the batter. Fold only 2 or 3 times, leaving swirls of pumpkin in the batter.
Pour the batter into the pan and smooth the top with a spatula. Place it on the middle shelf of the oven, and bake until the top is brown and a skewer inserted into the center comes out clean, about 45 to 50 minutes.
Cool the cake. Unmold it, and place it, right side up, on a serving plate.