Cook bacon until crisp. Set aside.
Heat 1 tablespoon of reserved bacon grease in an 8 inch cast iron skillet over high heat. Add sweet potato and cook, stirring occasionally, until brown. If potato starts to brown to quickly, reduce heat. Cook until tender, about 10 minutes.
While the sweet potato is cooking, preheat oven to 450 degrees F. Using a stand mixer with the whisk attachment, beat eggs and cottage cheese on medium speed for 5 minutes.
When the potatoes are just about done, add rosemary and cooked bacon, stir, and cook until heated through. Transfer to a separate plate.
With the heat on low, melt the butter in the cast iron skillet, ensuring entire bottom and sides are well greased. Pour half of the egg mixture into the pan. Top with the potatoes and bacon, trying to spread in an even layer. Cover with remaining egg mixture.
Allow frittata to cook on cooktop over low heat for about 8 minutes. Then, add cheddar cheese to the top of the oven and place in preheated oven. Cook in hot oven for 8-10 minutes, until the middle is just set. Remove from oven and cover with plate. Allow to rest, covered, for 5 minutes.
Serve hot or cold.