Preheat the oven to 325ºF. Line 16 muffin tins with cupcake liners.

In a bowl, sift together 6 tablespoons of the sugar, the cake flour and the pumpkin pie spice. Set aside.

In the bowl of a stand mixer fitted with the whisk attachment, combine the egg whites and cream of tartar. Beat until the eggs get foamy, then slowly add the salt and the remaining 6 tablespoons of sugar. Continue to beat until the eggs have stiff peaks.

Remove the bowl from the mixer, and 1/4 of the sifted flour mixture. Gently fold until almost incorporated, then add another 1/4 of the flour. Continue to fold, adding in the flour in 2 more batches. Gently fold in the pumpkin until no streaks remain.

Fill each muffin cup full of the batter. The batter should come all the way to the top. Bake until the cupcakes spring back when touched lightly, about 18 minutes. Let the cupcakes cool completely.

To make the frosting, beat the cream until it starts to thicken, then gradually add the powdered sugar and pumpkin pie spice. Add the pumpkin puree and beat until stiff.