Add the egg yolks and sugar to a medium-sized bowl. Use a hand mixer on low speed or whisk, and beat until the mixture is pale and slightly thickened, about 2 minutes.
Next, in a medium saucepan over medium-low heat, whisk together the milk, cream, ½ cup of sugar, and salt. Bring the mixture to a low simmer.
Now, once the cream mixture has started to simmer, whisk about ⅓ of the hot cream mixture into the yolk/sugar mixture. Whisk to incorporate, and now add another ⅓ of the mixture, stir again. Leave the remaining cream in the saucepan, gently simmering.
Return the egg/cream mixture back to the saucepan with the remaining simmering cream mixture, and stir to incorporate.
Using a wooden spoon, stir the mixture constantly over low heat until it thickens slightly and coats the back of the spoon. DO NOT boil, or the yolk will overcook...this only takes a few minutes.
Pour the mixture through a fine-mesh strainer and discard the vanilla pod. Bring to room temperature (you can place the bowl in an ice bath, without submerging, to expedite cooling).
Turn on broiler to high.
Place marshmallows on a shallow baking sheet lined with parchment paper and broil for 2 - 3 minutes (keep a close eye on them, they brown quickly). Remove from oven and quickly flip the marshmallows. Roast again, but be careful, they'll brown even faster the second time.
Let the marshmallows cool slightly, then place them in the blender.
Add the cooled custard to the marshmallows in the blender. And add another ½ cup of cream and the vanilla extract. Puree until well blended and smooth.
Pour into a bowl, cover with plastic wrap, and refrigerate 4 hours, or overnight (overnight is best).