Place egg whites in a small bowl (make sure there is no trace of egg yolk). Cover with plastic wrap and poke a few large holes in it. Leave out at room temperature for 8 hours or in the refrigerator overnight. Bring to room temperature before using.
Place confectioners' sugar and fine almond flour into a fine mesh sieve over a bowl. Sift and let the bowl catch the sifted ingredients. Discard any large clumps in the sieve. Repeat twice and set aside dry ingredients.
Put egg whites in a very clean bowl of a stand mixer fitted with a whisk attachment. Whisk eggs on medium-low speed for a minute or two until frothy then add the cream of tartar, pumpkin pie spice and salt. With the mixer running, very slowly add the bakers sugar (either 2 teaspoons at a time or in a very slowly sprinkle into the bowl). Increase speed to medium-high and beat until stiff peaks form, about 5 minutes on KitchenAid Stand Mixer speed 6. During the last minute, add the 2 drops of orange gel food coloring. Pro tip: The mixture will ball up in the whisk and the mixture will stay in the bowl if turned upside down.
Add half of the dry ingredients to the mixing bowl. Use a silicone spatula to gently fold the dry ingredients into the wet ingredients. Once mostly incorporated, add the remaining dry ingredients. Continue folding by going around the sides of the bowl with the spatula, then cutting through the center. The batter is done when it has a lava-like consistency. Do not over-mix. Pro tip: Try lifting the spatula out of the bowl and forming figure 8 with the batter without it breaking.
Transfer batter to a piping bag fitted with a round tip (about 1/2-inch in diameter). Pipe batter onto a silpat mat with macaron outlines or onto parchment paper. Pipe circles 1-inch wide and spaced 2 inches apart. Lift the baking sheet about 6 inches off the counter and drop it down. Repeat twice more, then rotate the pan 180° and bang the pans three more times (this releases air bubbles from the macarons). I also like to use a toothpick to pop any air bubbles I see at the top of the cookies.
Let the macarons sit at room temperature for 40 to 45 minutes and up to an hour. The macarons are ready to bake when dry to the touch (you should be able to "pet" them without leaving a mark).
Ten minutes before macarons are done drying, preheat the oven to 300° F. Bake macarons for 12 to 14 minutes, rotating the pan halfway through. Cool completely.
Decoration
Match up the cooled macarons according to size and determine which cookie you’d like to be the “top” with the jack-o-lantern face.
Place a small amount of black gel food coloring on a plate. In a small dish or bowl, add 2 teaspoons vanilla extract. Use a small tip brush and dip it into the vanilla extract, then gently swirl with the black food coloring to thin it out slightly.
Paint jack-o-lantern faces on the tops of the macarons shells and let them dry completely. Before adding the filling.
Filling
In the bowl of a stand mixer fitted with a paddle attachment, beat the butter and pumpkin purée until creamy, about 2 minutes. With the mixer on low speed, gradually add in the confectioners' sugar and pumpkin pie spice until completely incorporated.
With the mixer on medium speed, add the vanilla and a pinch of salt. Mix until combined. If necessary, add milk for a thinner consistency.
Assembly
Transfer frosting to a bag with the desired tip. Pipe buttercream on the bottom of one macaron shell. Top with the matching shell. Repeat with remaining cookies.
Notes
Almond flour: I find that Bob's Red Mill superfine almond flour yields the best results.Cream of tartar: This ingredient is essential for stabilizing the egg whites. It can be found in the baking aisle at your local grocery store.Egg whites: It's easier to separate the egg whites from the yolk while the eggs are still cold. It's essential that the egg whites have time to dehydrate overnight so there's not too much liquid in the batter.Clean the mixing bowl thoroughly before starting. There should be absolutely no residue (oil, grease, dust or water).Store macarons in an airtight container in the refrigerator for up to 5 days. They are best when eaten within 24 hours.Freeze macarons for up to 3 months. Use plastic wrap to wrap together groups of 4 or 5 sandwiches, then place them in an airtight container to prevent freezer burn. Defrost in the refrigerator before serving.