In a 9- or 10-inch cast-iron skillet or a large ovenproof skillet, melt butter over medium heat. Add onion, garlic and the remaining 1/4 teaspoon of the salt. Cook, uncovered, for 2 minutes, stirring occasionally. Add potatoes. Cook for 7 to 10 minutes or until potatoes are just tender and starting to brown, stirring occasionally. Spread vegetable mixture evenly across the bottom of skillet.