Arrange bacon on a 10-inch cast iron skillet (or other same sized oven-safe skillet) in a single layer. Set over medium heat. Cook to render bacon fat, about 5 minutes. Once bacon starts to color and there is enough oil in the skillet, add in chopped kale. Continue to cook and toss as needed until kale is tender and slightly wilted, about 3 minutes. Remove skillet from heat and set aside.
In a large bowl, whisk together red pepper flakes, eggs, milk, 1 ½ teaspoon kosher salt and 1 teaspoon freshly ground black pepper until well combined. Add in kale-bacon mixture, bread cubes, ½ cup parmesan cheese, fontina cheese, and rosemary. Toss to combine. Ensure bread is fully coated with egg mixture.
Preheat the oven to 350℉. Transfer contents back to the 10-inch skillet. Distribute contents into an even layer. Sprinkle remaining 2 tablespoons of parmesan on top. Let the mixture sit for 20-30 minutes while the oven preheats.
Bake for 40-45 minutes until the bread pudding has puffed up, the top layer of bread is toasted, and a knife inserted in the center of the pudding comes out clean.
Cool for 10-15 minutes. Serve warm with additional cheese, if desired.