Grease the inside of your slow cooker with butter and preheat on high 15 minutes.
In a large, heavy-bottomed pot, whisk together milk, cornmeal, and salt, and bring to a boil. Continue whisking another 5 minutes; then cover and simmer on low 10 minutes. Remove from the burner and add butter.
In a medium-size bowl, combine eggs, molasses, and spices. Add some of the hot cornmeal mixture to the egg mixture to temper the eggs; then transfer egg mixture into the pot. Stir in cranberries, if you like.
Scrape batter into the slow cooker and cook on high 2 to 3 hours or on low 6 to 8 hours. The center will be not quite set.
Serve warm topped with ice cream, whipped cream, or light cream.