Preheat oven to 375°F. Line a large baking sheet with parchment paper.
Fries
Wash potatoes (peel if desired) and cut into ½" fries.
In a large bowl, soak in cold water for at least 30 minutes. Remove and dry very well.
Toss with oil and salt. Spread on prepared pan in a single layer.
Bake for 20 minutes, then turn oven to 425° and cook fries until golden (about 20-25 minutes more)
Gravy
In a saucepan, cook onion in oil over medium heat until tender. Add garlic, tomato paste, seasonings, and cook for 2 minutes.
Stir in butter, add flour and cook for 5 minutes stirring constantly.
Add beef broth and 1 cup of water a bit at a time stirring after each addition until smooth. Bring to a boil, reduce heat to a simmer and cook for 2 minutes. Strain through a mesh strainer.
Assembly
Place fries on a serving plate and top with mozzarella cheese. Pour very hot gravy over the fries and cheese.
Serve immediately.
Notes
Soak the cut fries in cold water. Drain and dry them well before cooking.
Assemble disco fries just before serving to avoid the potatoes from becoming soggy.
Refrigerate leftover disco fries separately for 2-3 days.
Reheat fries in the oven, or on the stovetop. Gravy can be reheated in the microwave or on the stovetop. Once reheated, assemble as per directions and enjoy.