Preheat oven to 400 F and line a baking sheet with parchment paper. Toss the pears with the melted butter, vanilla extract, 2 teaspoons of sugar and a pinch of salt. . Spread the pears on the baking sheet and roast for 20 minutes. Allow to cool slightly then puree pears in a food processor or blender. I prefer to puree most of my pears. You can set aside about a half cup pear chunks, if you prefer to see some pears in the cake. Set aside. Reduce heat to 325 F.
In a medium sized bowl, whisk to combine the flour, cocoa powder, baking soda, cinnamon, nutmeg and salt. Set aside.
In a large bowl or the bowl of an electric mixer, cream together the butter, oil, and sugars until combined and creamy. Mix in the eggs one at a time. Scrape down the sides of the bowl after each addition. Add the vanilla. With a spatula, stir in the buttermilk and pears followed by the dry ingredients, stirring until just combined.
Spray a 10 cup bundt pan with a nonstick oil and flour spray such as Baker’s Joy. Spray in short strokes then use a pastry brush to brush the oil all around the pan. Be sure to coat all the nooks and crannies.
Pour batter into prepared pan. Bake at 325 F for 53 to 57 minutes, until a cake tester comes out clean or only with a few crumbs when inserted in the center or until cake springs back to the touch.
Remove cake from oven. Immediately set a timer for 10 minutes. Allow cake to cool slightly in the pan for 10 minutes then invert pan Cool in pan on a wire rack for 30 minutes then carefully invert cake onto a wire rack. Allow to cool completely.