In a small saucepan, bring the cream to a low boil. In a separate bowl, mix cornstarch and sugar. Pour the cream into the sugar slowly while stirring. Pour back into the small saucepan and let the mixture come to a full boil.

Add the pumpkin puree and the spices and whisk to combine. Roughly chop the white chocolate and place in a heatproof bowl. Pour the cream/pumpkin mixture over the chocolate and whisk until the chocolate is melted and fully combined. Let the ganache cool until warm and then stir in butter.

Cover the ganache with plastic wrap that is touching the ganache so as not to form a skin. Let the ganache cool at room temperature overnight.

Set out four eggs to mature overnight.

Line baking sheets with parchment paper or a silicone baking mat.

Whip egg whites on medium speed with a pinch of salt in a large bowl until foamy. Increase the speed and gradually add the sugar. Whip to stiff peaks.

Sift almond flour and confectioners sugar into the bowl. Gently fold into the egg whites with a spatula. The mixture should look like 'magma' and be able to draw a figure 8 with the spatula (see video below).

Put the mixture into a piping bag and pipe 1 inch circles about 2 inches apart on the parchment paper lined baking sheets. Tap the sheets 2-3 times against the counter to remove air bubbles. Let the macarons dry out for 1-2 hours at room temperature.

Once a "skin" has formed on top of your macarons, bake for 10 minutes at 325 degrees F with a spoon propping the oven door open slightly. Rotate the macarons halfway through baking so they bake more evenly. They are done when they easily lift off the parchment paper.

Let the macarons cool completely. Once cooled pair like-sized macarons together and pipe about a tablespoon of ganache onto the bottom shell and top with a matching top.