Step 1: Sift the 1 ¾ cups powdered sugar, almond flour, and pumpkin pie spice together twice. Discard any large almond pieces that remain in the sifter.
Step 2: In a large clean bowl, beat the egg whites and cream of tartar on medium speed until soft peaks form. Gradually add granulated sugar while continuing to beat on high until stiff, glossy peaks form.
Step 3: Add a small amount of orange gel food coloring and fold gently. Then, fold in the dry ingredients in three batches using a rubber spatula.
Step 4: Perform the macaronage: Fold the batter by scraping the sides and cutting through the middle until it reaches a lava-like consistency that flows in ribbons.
Step 5: Transfer the batter to a piping bag fitted with a round tip. Pipe 1.5-inch circles onto baking sheets lined with parchment paper.
Step 6: Tap the baking sheets firmly on the counter 5 times to release air bubbles. Let the shells rest at room temperature for 30-60 minutes until a skin forms.
Step 7: Bake at 300°F (150°C) for 15-18 minutes. Allow shells to cool completely before removing them from the parchment.
Step 8: Prepare the filling by beating the butter, reduced pumpkin puree, powdered sugar, and vanilla until light and fluffy. Pipe onto half the shells and sandwich with the remaining halves.