Place the yolks, sugar, cornstarch, and salt in a medium bowl and whisk to combine.
Heat the milk in a small pot until small bubbles form around the edge, and wisps of steam are rising from the surface.
Add the hot milk to the egg mixture, a little at a time, whisking to combine.
When all the milk has been added, transfer the mixture back to the pot and place over medium-low heat.
Cook the pastry cream, whisking, until thickened.
Remove from heat and stir in the vanilla.
Pour the pastry cream through a fine mesh strainer, into a heat-safe bowl. (Use the back of a ladle to press the mixture through the sieve.)
Press a layer of plastic wrap directly onto the surface, and refrigerate until completely cool (about 2 hours)
Whip the cream and powdered sugar together until stiff.
Fold the whipped cream, pumpkin, and spices into the pastry cream.