In a small saucepan, over low heat, warm the milk. Don’t boil it -- bring it to almost boiling and then turn off the heat.
In a large heavy pan, such as a Dutch oven, over low heat, melt butter. Once it is melted, add the rice and cranberries and stir to coat and slightly toast the rice, or about 1-2 minutes.
Ladle in about 3/4 cup of the warm milk and continue to stir. Once the rice has absorbed the milk, add another ladle of milk. Continue this process–stirring nearly continuously until the rice is tender (taste it!) and your milk is almost gone, about 25 minutes. Make sure to watch out for the cranberries–they like to pop!
Add the final bit of milk, the sugar, cinnamon, and vanilla bean. Stir until all ingredients are incorporated.