Next, heat the olive oil in a skillet on medium heat. Add the onions and cook until they are starting to soften. Add the garlic and the sausage, letting the sausage pieces brown on each side.
Add 1 Tablespoon of the butter to the pan and let it melt. Continue cooking until the butter begins to brown very slightly. Remove from the heat.
To prepare the kale, place the cooked kale, egg, 1/2 cup of the ricotta, the salt, pepper, Italian herbs and pepper flakes in a large bowl. Stir in 1/3 cup of bread crumbs and 1/4 cup of the parmesan cheese. Mix until well blended.
Place the kale mixture in the bottom of a casserole dish. Top it with the sausage mixture.