Bring a large pot of salted water to a boil. Cook the noodles, drain and set aside.
Heat a medium saucepan over medium heat and add 3 butter pats. When the butter has melted, stir in the garlic and onion powders and flour and cook while stirring for 3 minutes. Slowly whisk in milk and broth and continue cooking until it thickens slightly. Add salt and pepper. Pour the sauce over the noodles and stir in the tuna.
Pour into a 9 by 13 baking dish, cover with foil and cook for 20 minutes. Melt the remaining 3 butter pats and mix them with the crackers. Remove casserole from the oven and sprinkle with crackers. Bake uncovered for an additional 5 to 7 minutes.