Arrange 6 fully baked brownie mounds, each 1 1/2–2 inches wide, on a lined tray. Freeze for 30–45 minutes until firm. Line baking sheets with parchment.

Beat 1 cup softened butter, 1 cup granulated sugar, and 1/2 cup packed brown sugar until fluffy. Mix in 1 large egg, 1 egg yolk, 1 cup pumpkin puree, and 2 teaspoons vanilla.

Whisk together 3 3/4 cups plus 2 tablespoons flour, 2 teaspoons espresso powder, 1 teaspoon baking soda, 1 teaspoon baking powder, 1/2 teaspoon salt, 2 teaspoons pumpkin pie spice, 1 teaspoon cinnamon, and 1 tablespoon cornstarch. Gradually mix into the butter mixture just until combined. Chill 20–30 minutes if sticky.

Measure 3 cups dough into 12 portions of 1/4 cup each. Reserve the remaining dough separately. Flatten 1 portion slightly, add 1 frozen brownie center, and cover with a second 1/4-cup portion. Seal every edge and shape into a tall dome. Repeat for 6 cookies.

For sugar-coated cookies, mix 1/2 cup granulated sugar, 1 teaspoon cinnamon, and optionally 1/4 teaspoon espresso powder. Roll all 6 assembled cookies in the mixture and discard leftover coating. For the Nutella finish, leave the cookies plain at this stage.

Freeze all 6 assembled cookies for 30–60 minutes until firm. Heat the oven to 350°F. Arrange cookies about 3 inches apart on lined sheets; bake one sheet at a time, keeping the remaining cookies frozen.

Bake the 6 cookies at 350°F for 18–25 minutes as a starting range, until the edges are set and lightly golden and the pumpkin dough no longer looks wet. Allow roughly 2–3 additional minutes for fully frozen cookies and check the dough for doneness. Loosely cover with foil if browning before the dough sets.

Rest each batch on its baking sheet for at least 15 minutes, then transfer carefully to a rack. For the Nutella finish, cool the cookies, warm enough Nutella to drizzle, and spoon it over the tops. Let the drizzle settle before packing.