Pour the heavy cream and sugar into a saucepan and bring to a simmer over medium heat, stirring frequently.
In a bowl, whisk the egg yolks with the pumpkin, vanilla extract, cinnamon, ginger, nutmeg, and salt. Whisk about 1 cup of the hot cream mixture into the egg yolk mixture and then return egg yolk mixture to the saucepan. Cook, stirring, until the custard mixture coats the back of a spoon, or to about 170 F.
Add 1 cup of water to the inner pot of the Instant Pot and then place a trivet in the pot.
Pour the custard mixture into 5 ramekins (around 5 ounces each). Cover the ramekins tightly with foil and arrange them on a baking sling in 2 layers.
Lower the ramekins onto the trivet and fold the ends of the sling over them.
Place the lid on the pot and ensure the steam release knob is in the sealing position. Choose pressure cook or manual (high pressure) and set the timer for 12 minutes.
When the time is up, let the pressure come down naturally for 15 minutes and then carefully release the remaining pressure.
Remove one of the ramekins and check it for doneness. It will jiggle slightly in the center. If the center still appears liquid, replace the foil and return the ramekin to the pot. Cook at high pressure for another 2 to 3 minutes and then do a quick release and check again.
Uncover the ramekins and place them on a platter or baking sheet. Refrigerate the custards for at least 3 to 4 hours or overnight.
Just before serving, sprinkle about 1 to 1 1/2 teaspoons of superfine sugar over the top of one of the custards. Slowly move the flame of a blowtorch over the sugar until golden brown and caramelized. The ramekin edges will be quite hot, so be careful when moving or turning them.
The sugar will harden within a few minutes.
Serve immediately with whipped cream and cinnamon sugar, if desired.