In a large bowl, combine potatoes, squash, onion, egg, flour, garlic salt, salt, and pepper. If the batter is too thin, add more flour; if too thick, add milk. Form batter into 3-inch patties.
Cover the bottom of a large skillet with just enough oil to cover the bottom of the pan, and heat over medium-high heat. Place patties in hot oil, and cook until golden brown on each side; drain on paper towels.
