1 cup butter, plus more for the pan
1 cup packed light brown sugar
2 tbsp light corn syrup
3 1/2 cups rolled (old-fashioned) oats
9 in (23cm) square baking pan
Preheat the oven to 300F (150C). Lightly butter a 9in (23cm) square baking pan. Heat the butter, brown sugar, and syrup in a large saucepan and stir over medium-low heat until the butter has melted. Remove from the heat and stir in the oats. Spread evenly in the pan. Bake for 40 minutes, or until evenly golden and just beginning to brown at the edges. Transfer to a wire rack and let cool 10 minutes. Cut into bars and let cool completely.