Preheat oven to 425° F. Line 9 X 13 inch baking dish with parchment paper.
Melt 1/4 cup (1/2 stick) butter in medium saucepan. Pour melted butter into prepared baking dish. Spread butter around bottom of dish and arrange crackers over butter, breaking crackers to fit empty spaces if needed.
Melt remaining 1 cup (2 sticks) butter in same saucepan; add sugar. Bring to a boil over medium heat. Reduce heat to low; cook, stirring occasionally, for 2 minutes. Remove from heat; stir in sweetened condensed milk. Pour over crackers.
Bake for 10 to 12 minutes or until mixture is bubbly and slightly darkened. Remove from oven; cool for 1 minute.
Sprinkle evenly chocolate chips and let stand for 5 minutes; spread evenly. Optional; sprinkle with nuts. Cool in pan on wire rack for 30 minutes. Refrigerate for 30 minutes or until chocolate is set. Remove from parchment paper; cut into pieces.
You can substitute graham crackers for the saltine crackers.
If using nuts, you can substitute pecans for walnuts.
You can substitute heavy-duty aluminum foil for parchment paper.