Preheat the oven to 350℉. Line a rimmed baking sheet with foil (to catch anything that might bubble over).
In a 12-inch ovenproof skillet set over medium heat, melt 1 tablespoon of the butter. Add the peaches and ¼ cup of the brown sugar. Cook, stirring, until the juices thicken into a light syrup, about 8 minutes. Remove the pan from the heat.
In a medium bowl, combine the remaining 4 tablespoons of butter, the remaining ½ cup brown sugar, flour, pecans and salt. Spread the mixture evenly over the peaches. Place the skillet on the lined baking sheet.
Bake until golden brown and bubbly, about 30 minutes. Serve warm with vanilla ice cream, if desired.