Pumpkin swirl brownies

Directions

1. Set your oven to 350°F. Line a 9x11-inch baking pan with parchment paper, letting it overhang on two opposite sides. Butter the uncovered sides well and lightly butter the parchment.
2. In a double boiler (or a heatproof bowl over a pot of barely simmering water), melt 1 stick unsalted butter and 6 oz. bittersweet chocolate chips, stirring until smooth. Set aside to cool slightly.
3. In a medium bowl, whisk together 2 cups all-purpose flour, 1 teaspoon baking powder, and 1/2 teaspoon sea salt. In a large bowl (or the bowl of a stand mixer with the paddle attachment), combine 1-1/4 cups sugar, 4 large eggs, and 1 tablespoon pure vanilla extract. Beat until fluffy and well blended, about 3-5 minutes on medium speed. Add the flour mixture and beat just until incorporated.
4. Divide the batter evenly between two bowls (each should have about 2 cups). To one bowl, stir in the melted chocolate mixture until combined. To the other bowl, add 1-1/4 cups pumpkin puree, 1/4 cup olive oil, 1-1/2 teaspoons ground cinnamon, 1/2 teaspoon ground ginger, 1/4 teaspoon ground nutmeg, and 1/8 teaspoon ground cloves. Stir until uniform.
5. Pour half of the chocolate batter into the prepared pan and spread it evenly. Spoon half of the pumpkin batter on top and spread gently. Repeat with the remaining chocolate and pumpkin batters, layering them.
6. Take a butter knife and insert it into the batter nearly to the bottom. Gently swirl the knife through the pan in a figure-eight or zigzag motion to create a marbled pattern.
7. Bake for 35 to 38 minutes, or until the brownies start pulling away from the pan edges and a toothpick inserted in the center comes out clean.
8. Let the brownies cool completely in the pan. They are best served cool and taste even better the day after baking.