- In a large saucepot, sweat onions in butter until translucent.
- Add salt, cayenne pepper, rosemary, and half and half. Bring to a boil. Add the corn and granulated sugar. Bring back to a boil, then reduce heat to a simmer for 10−15 minutes, stirring frequently.
- In a cup, mix the corn starch and water to make a slurry. Add slurry to pot and stir well. Allow slurry to thicken slightly, then remove from heat.
- Remove rosemary, allowing a few leaves to remain but no stem. Using a ladle, remove about half of the corn mixture and place into a blender on pulse until smooth. Add blended corn mixture back to the pot and combine well. Check seasoning and serve warm or chill and store for up to four days.