1/2 cup (1 stick) unsalted butter, at room temperature
1/2 cup vegetable oil
2 1/4 cups light brown sugar
1 1/4 cups fresh butternut-squash puree (see recipe)
1 tablespoon vanilla extract
2 teaspoons grated lemon rind
4 1/2 cups flour
1 tablespoon cream of tartar
1 teaspoon baking soda
1 teaspoon baking powder
1/2 teaspoon salt
2 tablespoons ground cinnamon
2 teaspoons freshly grated ginger
2 teaspoons ground allspice
1 1/2 cups quick-cooking oats
Set the oven at 350 degrees. Have on hand two ungreased baking sheets.
In the bowl of an electric mixer, cream the butter. Add the oil, brown sugar, and squash puree and beat thoroughly. Add the eggs, one at a time, followed by the vanilla and lemon rind. Beat for 1 minute.
In another bowl, mix together the flour, cream of tartar, baking soda, baking powder, salt, cinnamon, ginger, and allspice. Add the dry ingredients to the squash mixture and mix just until the batter is moist. Stir in the oats.
Using a soup spoon, spoon 24 mounds of the batter onto the baking sheets. Moisten your hands with water and gently press the mounds so they spread to 3 inches.
Transfer the cookies to the oven and bake for 15 minutes or until they are just firm.