Place sliced bread in a shallow baking dish or bowl, and drizzle with milk to saturate. Let sit for 30 minutes, gently flipping occasionally to ensure even soaking.
Meanwhile, warm a large cast iron pot (6 - 8 quarts) over medium-high heat. Add sausage and cook, stirring often to crumble, until lightly golden (10 - 15 minutes). Stir in the onion, celery, parsley and garlic along with a pinch of kosher salt and several turns of black pepper. Cook until the onion and celery soften (5 to 8 minutes), stirring occasionally. Add kale, 1/2 cup water and a pinch of kosher salt, and cook until the kale wilts (about 5 minutes). I like to switch to tongs here to easily mix up the kale and the sausage mixture.
Using your hands, break up the bread into bite sized pieces, then place in a large bowl. Add the sausage-kale mixture to the bowl along with the Parmesan cheese, basil, sage, rosemary, 2 pinches of salt and several turns of black pepper. Gently toss the mixture until all ingredients are evenly incorporated (I like to use my hands here). Season to taste with additional salt and pepper. Spoon stuffing into a 9 by 13 baking dish.
Preheat an oven to 350°F. Bake uncovered until hot (at least 150° in center) and lightly browned (25 - 30 minutes).