For the macaron shells:
6 oz. slivered or blanched almonds
1½ oz. chopped pecans
9¾ oz. confectioners’ sugar
1 oz. (1 tbsp.) pumpkin pie spice
3 large egg whites (about 100 grams)
1½ tsp. cream of tartar
For the pumpkin pie filling:
1¼ cups pumpkin puree
6 tbsp. packed light brown sugar
¼ cup granulated sugar
2 tsp. all-purpose flour
¼ tsp. salt
1¼ tsp. pumpkin pie spice
1 large egg plus 2 egg yolks
½ cup heavy cream
2½ tbsp. milk
½ tsp. vanilla extract
To make the macaron shells, line two baking sheets with silicone baking mats or parchment paper. Have a pastry bag fitted with a large round tip ready (I use Ateco #809). In the bowl of a food processor, combine the almonds and pecans. Pulse until mostly well ground. Add the confectioners’ sugar and pumpkin pie spice to the bowl and continue to process in brief pulses until the nuts are finely ground and the mixture is even. Set aside.
In the bowl of a stand mixer fitted with the whisk attachment, combine the egg whites and cream of tartar. Whip on medium-high speed until stiff, glossy peaks form, about 3-4 minutes. Add about one third of the ground nut mixture to the bowl with the egg whites and fold in gently with a spatula. Fold in the remaining nut mixture in two additions, just until the ingredients are combined and no lumps or streaks remain. The batter will be fairly thick. Transfer the mixture to the pastry bag. Pipe 1-inch circles, about ½-inch thick, onto the prepared baking sheets spacing them about 1 inch apart. (They will spread slightly after piping but don’t worry.) Allow the cookies to rest at room temperature uncovered for 2 hours. (This step helps the cookies develop the delicate exterior crust and “foot” on the bottom.)
Preheat the oven to 300˚ F and set oven racks in the the lower half of the oven. Bake, rotating the pans halfway through baking, until the macarons appear set but are not browned, about 12-14 minutes. Let cool. (To ensure adequate drying of the cookies, I like to shut off the oven at the end of baking, prop the door open slightly with a wooden spoon, and let the shells cool slowly in the oven.) Once the cookies are cool, carefully remove them from the baking mats and transfer to a wire rack, matching them up in pairs by size.
To make the filling, preheat the oven to 350˚ F. Combine the pumpkin puree, sugars, flour, salt and spices in a medium bowl. Whisk in the egg and egg yolks, then the cream, milk and vanilla until the mixture is smooth and well blended. Pour into a small lightly greased baking dish (I used a 9-inch oval baker). Bake about 50 minutes, rotating halfway through, until just set and the mixture no longer jiggles in the center when the pan is gently shaken. Let cool on a wire rack completely, at least two hours.
Scoop the baked pumpkin pie filling into a mixing bowl and beat briefly with an electric mixer just until smooth, about 20-30 seconds. Transfer to a pastry bag fitted with a plain round tip. Pipe a small dollop of the pumpkin pie mixture onto the flat side of one cookie of each pair. Sandwich together with the remaining cookie, pushing the filling to the edges. Store in an airtight container.