Preheat oven to 350 degrees F.
Swirl olive oil in 10-inch cast iron skillet to coat the pan. Heat oil over medium heat. Add bacon and let cook until bacon fat has rendered. Add in chopped kale. Season with a little salt and pepper. Cook, tossing, until kale is tender and slightly wilted. Taste kale to make sure it is cooked.
In a large bowl, whisk together red pepper flakes, eggs, milk, about 2 tsp salt, and 1 tsp fresh ground black pepper. Add cooked kale and bacon, bread cubes, 1/2 cup parmesan, 1/4 cup fontina and 1 tsp fresh rosemary. Toss to combine and ensure bread is coated with egg mixture.
Transfer to 10-inch skillet used to cook bacon and kale. Distribute to make an even layer. Sprinkle top with remaining 2 Tbsp parmesan. Bake for 30-40 minutes until bread pudding has puffed up, top layer of bread is toasty, and pudding is set in the center. Serve warm with additional parmesan cheese.