Clean your kale by rinsing it in cold water and then removing the leaves from the stems. Chop into small pieces.
Heat olive oil on medium in a cast iron skillet or another large skillet (with a lid). Add onion and garlic and cook for approximately 90 seconds.
Add kale and coat with oil and mix with garlic and onion. Let saute for another minute, add 1 teaspoon of salt, mix, and then add the stock. Cover and let braise in stock for about 10 minutes, or until most of the stock has cooked off.
Meanwhile, bring 3 quarts of water to a boil. Add noodles and boil until al dente. Drain and rinse in cold water to prevent sticking.
When your kale is done, remove from skillet and set aside.
WIth skillet on medium, add butter and as it melts, add the flour and whisk to create a roux.
Slowly add the milk, 1 cup at a time, and whisk it to incorporate it all before adding more milk and half and half.
Let the sauce cook, whisking constantly to prevent from burning, until it begins to thicken. Add cheese, 1 cup at a time, and whisk to combine. Reduce to medium-low.
Let the sauce thicken and then start adding the cheese, a handful at a time, whisking until it is all fully melted before adding more cheese. Repeat for 2 cups of cheese.
Once cheese sauce is thickened, add 1/2 teaspoon salt, pepper, and mustard and mix. Add kale and mix well. This will ensure that the kale is more evenly distributed in the dish.
Once the kale is well mixed in, then add the cooked pasta and mix well.
This is where you can stop and set aside if preparing in advance. Or you can serve it now, as is. Otherwise, pre-heat oven to broil and set rack to top third.
Add last 1/2 to 1 cup of cheese to the top of skillet and add to oven to melt and crisp up cheese for 3-5 minutes.
Serve and enjoy!