In a heavy saucepan, add your cream and turn heat to just above medium. Add pumpkin pie spice (or whole spices, if using) and let steep for 15 minutes. You do not want this to boil or bubble.
1 cup heavy whipping cream, 2 tablespoons pumpkin pie spice
Remove from heat and strain whole spices, if using. Add the sweetened condensed milk and stir. Add the pumpkin puree and vanilla and gently whisk to incorporate. Do not beat, just ensure the pumpkin puree is well distributed.
If you do not have pumpkin pie spice, you can use whole spices. A full cinnamon stick (or 1 1/4 teaspoon), 6 whole cloves, 1/2 teaspoon freshly grated ginger, and 1/2 teaspoon freshly grated nutmeg. Depending on your preference, if you use whole spices, you may or may not want to add a touch more ground cinnamon at the end.
For more tips and tricks, be sure to read the full article above.