Preheat oven to 350 degrees.
Line 9x13 with nonstick foil hanging over sides.
Combine flour, sugar, and salt in medium bowl.
Add melted butter and stir with rubber spatula until flour is evenly moistened.
Crumble dough evenly over bottom of prepared pan. Using your fingertips and palm of your hand, press and smooth dough into even thickness. Using a fork, pierce dough at 1-inch intervals.
Bake until light golden brown approx 25 mins. Cool 20 mins while you make the caramel.