Wash and dry 4 large baking potatoes (russets). Place on a foil lined baking sheet. Using a fork, prick holes all over the potatoes about 8 times each potato. Sprinkle with salt. Bake in preheated oven at 450 degrees for 60 - 75 minutes until potatoes are tender. Remove from oven and allow to rest.
In a medium skillet melt butter and saute onion until softened over medium high heat. Break in ground beef and cook until browned and no longer pink. Drain excess grease.
Stir in taco seasoning and broth, simmer for a few minutes. Turn off heat.
Slit potatoes lengthwise and scape out potato pulp from the skin and place into medium bowl. Add sour cream, milk, and 1 cup of cheese to potato pulp and mix well.
Add potato mixture to ground beef mixture and stir to combine. Stuff 1/4 of the combined mixture into each potato, mounding high. Sprinkle with extra cheddar cheese.
Spray a 9 x 13 baking dish with non-stick cooking spray. Place potatoes into baking dish. Bake in preheated oven at 350 degrees for 20 minutes until cheese has melted.
Top with your favorite taco toppings. (Sour cream, cilantro, pico, picante sauce, queso fresco, etc.)