In a medium saucepan, bring the cream to a boil over medium heat.
Immediately turn off the heat, stir in the vanilla, and set aside.
Whisk egg yolks and sugar until light and fluffy.
In a separate bowl, whisk 1/4 cup hot cream and cornstarch, until perfectly smooth.
Add the cornstarch mix to the eggs, and keep whisking.
Add 1/4 cup of the hot cream at a time, constantly whisking.
Pour the mixture through a strainer into the saucepan on med-high heat.
Stir in the pumpkin puree, and bring to a boil, constantly whisking.
Keep whisking until the mixture comes to a slow boil.
Remove from heat, stir in the butter.
Let stand 5 minutes, cover with clingwrap pressed against the entire surface, and chill at least 2 hours.