6 kale leaves, stemmed, cut into 1-inch pieces
4 cups whole milk
3 1/2 cups water
2 cups polenta
1/2 teaspoon salt
3/4 teaspoon ground black pepper
4 ounces pancetta (Italian bacon) or bacon, coarsely chopped
4 ounces mushrooms (such as crimini, oyster, and stemmed shiitake), sliced
4 tablespoons extra-virgin olive oil, divided
1 garlic clove, minced
1/2 cup low-salt chicken broth
2 tablespoons chopped fresh thyme
1 tablespoon grated lemon peel
4 tablespoons unsalted butter
2/3 cup freshly grated Parmesan cheese
Cook kale in large pot of boiling salted water until tender, about 6 minutes. Drain.
Bring milk, water, polenta, salt, and pepper to boil in heavy large saucepan over medium heat, whisking constantly. Reduce heat to low and simmer until thick, stirring occasionally, about 20 minutes. Remove from heat.
Meanwhile, cook pancetta in heavy large skillet over medium-high heat until golden brown, about 3 minutes. Using slotted spoon, transfer pancetta to paper towels. Add mushrooms and 2 tablespoons oil to drippings in skillet. Sauté until mushrooms are tender, about 6 minutes. Stir in kale and pancetta. Add garlic and broth; simmer until broth is slightly reduced, about 6 minutes. Stir in thyme, lemon peel, and 2 tablespoons oil. Season to taste with salt and pepper.
Whisk butter and Parmesan into polenta and divide among plates. Top with kale mixture.