Bring a large pot of water to boil. Place kale in the boiling water and continue to boil for 8 minutes. Drain and squeeze excess moisture out of kale (this can be done a day or two ahead and time. Just store the kale in the fridge until ready to continue with the recipe).
Melt the butter in a large sauté pan over medium heat. Add the shallots and cook, stirring frequently until just turning brown on the edges, about 10 minutes. Stir in the garlic and cook for about 30 seconds. Stir in the arrowroot flour and then the milk and cream. Continue to cook, stirring constantly, until the mixture begins to thicken, about 2-3 minutes. Add the crumbled saffron (if desired), and then stir in the kale until it’s coated with the creamy milk mixture. Continue cooking until the kale is heated through. Stir in the salt and pepper. If the mixture is too thick, you can thin it with a little milk. Taste and see if kale needs a bit more salt or pepper. Serve.