- 4 1/2 cups all-purpose flour
- 1 1/2 teaspoons baking powder
- 1 teaspoon baking soda
- 1 teaspoon salt
- 3 sticks (3/4 pound) unsalted butter, softened
- 1 1/3 cups creamy peanut butter
- 2/3 cup granulated sugar
- 2 1/4 cups packed brown sugar
- 1/3 cup vegetable oil
- 3 large eggs plus 2 large yolks
- 2 tablespoons pure vanilla extract
- Preheat oven to 350°F with racks in upper and lower thirds.
- Whisk together flour, baking powder, baking soda, and salt in a bowl.
- Beat together butter, peanut butter, sugars, and oil with an electric mixer at high speed just until pale and creamy, about 2 minutes in a stand mixer or longer with a handheld. Add whole eggs, yolks, and vanilla and beat until just incorporated. Reduce speed to low, then add flour mixture in 3 batches, mixing until well incorporated.
- Scoop scant 1/4cups of dough about 2 inches apart onto 2 ungreased large baking sheets. Flatten mounds with floured tines of a fork, making a crosshatch pattern, into 2 1/2-inch cookies (about 1/2 inch thick).
- Bake, switching position of sheets halfway thourough baking, until slightly puffed and golden around edges, about 30 minutes total. Transfer cookies to racks to cool.
- Switch an oven rack to middle position and make more cookies with remaining dough on a cooled baking sheet.