I followed this recipe http://www.averiecooks.com/2011/12/chocolate-saltine-toffee.html almost exactly, except I did use a jelly roll pan which measures 10 inches by 15 inches. I did not have overflow because when I lined the pan with foil I brought it up higher than the sides of the pan.
Although the recipe states 1 1/2 to 2 cups of chocolate chips, I needed all of the 2 cups and even broke up a few Hersey bar miniatures to add more chocolate. That might have been because my pan was bigger, but my advice is to be prepared to use the greater amount.
The hardest thing about this recipe is standing at the stove and stirring the toffee. Don't walk away. It comes to a boil very quickly and then you need to let it cook for about 4 minutes or more, stirring constantly.
I did have to spread the toffee about on the crackers to distribute before putting on the chocolate chips. I put the tray back into the warm oven to melt the chocolate faster just for a minute and then spread it about.
I did put it into the refrigerator to cool and harden.
Then you break off a corner to test it, and keep testing until you realize you have eaten five chunks of the stuff and you need to stop before it's all gone.
My supply is in the fridge.
What's left of it.