4 cups half and half
1 3/4 cups white sugar
2 Tbsp corn starch
2 more cups half and half
2 cups heavy cream
2 tsp vanilla extract
Bring 2 cups half and half to scalding (200 degrees) and while it's heating up mix in the sugar.
Add the corn starch mixed in a bit of cold half and half.
Whisk to thicken slightly, being careful not to boil.
Remove from heat, cool a bit, and add the remaining half and half, cream, and vanilla.
Chill to near freezing and churn; then move to freezer to firm up.