Source: Bookends Cafe, Boulder, Colorado

Crust and Topping
2 pounds all-purpose flour (about 6 cups)
12 ounces granulated sugar (about 1 3/4 cups)
1 pound 4 ounces butter (2 1/2 cups)

Filling
1 pound (4 sticks) butter
1/2 cup corn syrup
2 cups sweetened condensed milk
2 pounds brown sugar
1 cup chocolate chips

To make the crust and topping: Cut butter into the dry ingredients in a mixer, stopping once the ingredients develop a cornmeal-like texture. Reserve four cups of the mixture for topping. Press the remaining mix into the bottom of a greased, 12 x 18-inch pan. Bake at 300 degrees F until golden.

Bring butter, corn syrup, milk and brown sugar to a boil in a saucepan, whisking constantly. Whisk at "lava" boiling stage for five minutes. Pour over baked crust. Sprinkle remaining topping and chocolate chips on top. Bake at 300 degrees F until the filling in the middle of the pan is bubbling and golden brown, about 35 to 40 minutes. Place another pan on lower rack to catch any drippings. Cool before cutting.