Heat up the oven to 180 degrees C/350 degrees F.
In a large skillet, melt some butter and fry the onion, garlic and kale until slightly soft.
Add in the ground meat. Cook until brown.
Add salt, pepper, tomato purée, cayenne pepper, basil and oregano. mix and let cook for another few minutes.
Pour the meat into a large baking dish and spread out evenly.
Mash the cooked sweet potatoes with butter, salt and pepper until smooth. If the mash is too thick, add some broth or filtered water until desired texture. (I use a handheld mixer for this step.) Add 100g of the cheddar cheese here if you choose to include that.
Spread the mashed sweet potatoes evenly over the meat. (Sprinkle the remaining cheese on top)
Bake in the middle of the oven for about 30 min.