In a large saute pan, heat the olive oil over medium heat. Add the onions and saute until translucent, about 3 minutes. Add the garlic and kale, season with salt and pepper, to taste, and cook until wilted. Set aside to cool.
Once the mixture has cooled, add to a food processor and process until very smooth. Add a little water, if necessary, to help make a smooth mixture.
In another large pot, bring 5 cups of water and 2 cups heavy cream to a boil over medium heat. Whisk in the polenta and stir constantly until the polenta is creamy, about 20 minutes. If the mixture becomes too thick, add a little more water or cream.