A fast seller at bake sales, these are very rich and very sweet.
Preheat the oven to 350 degrees F.
To make the crust, combine the flour, ½ cup butter, and 1 cup brown sugar. Pat firmly into a 9-inch by 13-inch baking pan. Sprinkle the pecans over the crust.
To make the caramel layer, combine the ⅔ cup butter and ½ cup brown sugar in a small saucepan and boil for 30 seconds to 1 minute. Or put in a deep microwave-safe container and cook on high for 2 to 3 minutes, until bubbly. Pour over the nuts.
Bake for 18 to 22 minutes or until the top is bubbly. Remove from the oven and sprinkle the chips on top. When the chocolate has melted, swirl it in with the tip of a knife. Cut into squares when completely cooled.