In a small bowl mix together, heavy cream, corn starch and egg yolks. Whisk well to combine without any clumps.
Heat up milk in a microwavable container for about 2 minutes or until hot but not boiling. Set aside.
In a medium saucepan over medium heat, melt butter. Add brown sugar and use a spatula to stir constantly until brown sugar melts. Slowly add in warm milk, it may spatter a little when it hits the pan so add carefully. Use a wire whisk to continually stir in the milk. Add in the salt.
When the milk mixture begins to simmer just barely, add a couple tablespoons of the hot milk mixture to the cornstarch and egg yolks. Use a small whisk or fork to temper and mix this together. Add a couple more tablespoons of the hot milk then, pour the cornstarch mixture into the saucepan. Cook, stirring constantly, over medium heat until it starts to bubble. Cook for 1-2 minutes once its bubbling and it starts to thicken.
Remove from heat and stir in the vanilla extract. Continue to whisk for a minute or so after you remove it from the heat.
Serve warm or transfer to containers that you can store in the fridge (jars work well).
