8 tablespoons (1 stick) unsalted butter
1/2 cup packed dark brown sugar
1/4 cup granulated sugar
1/2 cup pumpkin purée
1 large egg, lightly beaten
4 teaspoons vanilla extract
1 1/2 cups bread flour
1 1/2 cups old-fashioned or rolled oats (not instant)
1 teaspoon ground cinnamon
1 teaspoon baking soda
1/4 teaspoon kosher salt
1 cup semisweet chocolate chunks or chips
In a microwave-safe bowl, melt the butter for 45 seconds. (This is just enough time to liquify most of the butter, but not heat it.) Stir with a fork to finish melting. (If you don’t have a microwave, melt on the stovetop until almost melted, but not quite. Remove from heat and continue stirring to cool.)
Combine the butter, brown sugar, and granulated sugar in a large bowl. Mix with a wooden spoon until the mixture is smooth. Add the pumpkin purée, egg, and vanilla, and stir until blended. Add the flour, oats, cinnamon, baking soda, and salt, and mix until almost combined, with a little bit of flour still visible. Fold in the chocolate chunks.
Grab a handful of dough (approximately 3 1/2 ounces) and place on a large plate or sheet pan; the mounds should be tall and craggly. (You should get 8 or 9 dough balls.) Freeze for 1 hour or refrigerate overnight.
Preheat oven to 375°F. Line a baking sheet with parchment paper or a silicone baking mat. Transfer half of the dough balls to the baking sheet, leaving about 2 inches around each one. Bake the cookies for 16 to 20 minutes, until light golden-brown, but still a little soft-looking on top (err on the side of underdone; do not overcook, as the cookies will continue cooking while cooling.) Let the cookies cool on the baking sheet for 10 minutes, and then transfer to a wire rack or large platter for another 4 hours to allow the cookies to completely set and develop their flavors. Repeat with the remaining dough.
These cookies keep beautifully in an airtight container for up to 5 days.