1. Combine rhubarb, 3/4 c. sugar, and water in a saucepan. Cook on medium-high heat until rhubarb is broken down, skimming off foam. (About 15-20 minutes.) Puree mixer in blender/food processor. (Confession: I added a few drops of red food gel at this point, to up the color factor a touch...rhubarb can get that brown look going, which is unattractive. Delicious, but ugly.) Place rhubarb puree in fridge, stirring occasionally until cool--about two hours.
2. In a small dish, whisk together the corn starch and 2 tbls. of the milk. In a saucepan, combine the cream, remaining milk, and rosemary sprigs. Bring to a boil then simmer for about 5 minutes, before turning off the heat and allowing the rosemary to steep. The longer you do this, the more intense the flavor...I ended up letting it sit for about half an hour.
3. Bring the milk/cream mixture back up to a simmer, add the remaining 1/4 c. of sugar, stirring to dissolve. Remove the rosemary sprigs and whisk in the corn starch slurry (it will thicken pretty quickly...don't stop whisking!), remove from heat, and add the cream cheese, stirring until it is melted through.
4. Whisk the cooled rhubarb puree to the cream, then place in the fridge to cool for several hours/overnight.
5. Pour into your ice cream maker and follow the manufacturer's instructions.
6. Once churned, pour soft serve into a container and freeze for several hours, saving some to eat at the kitchen counter, for breakfast.