In a medium saucepan combine the heavy cream, half and half, vanilla bean, rosemary sprigs, sugar, and salt.
Heat on medium-low until the sugar is melted. Stir occasionally.
Continue to cook about 2 minutes.
Remove from the heat and let it sit for a few minutes.
Remove the rosemary and vanilla bean.
In a medium bowl whisk the egg yolks.
Slowly whisk the hot mixture into the egg yolks. (Slowly so the heat doesn't scramble the egg.)
Return the mixture to the pan and cook over low heat until the mixture thickens slightly, about 4 to 5 minutes.
Pour the mixture into a glass bowl, cover with plastic wrap and refrigerate for at least 5 hours.
Remove mixture from the refrigerator and pour into the bowl of an ice cream maker and process until frozen.
Store in a freezer safe container in the freezer until ready to serve.