My recipe is 1 lb. of butter, 2 cups packed golden brown sugar and a 400 g box of Graham crackers. As someone mentioned, it can also be done with regular saltine crackers but I like the firmness of the Graham crackers.
I cut my butter into about 1inch slices and put it into a medium saucepan. I melt the butter and then add the 2 cups brown sugar. I bring it to a boil stirring constantly and it will combine as it boils. Boil for 3-4 minutes stirring. This mixture is poured over the crackers and spread. The pans then go into a 350* oven for 8-10 minutes. I use jelly roll pans (half inch sides) and do a solid layer of the crackers to prevent them from moving as I pour and spread the toffee. The crackers move around a bit as they cook in the oven and I moved them onto waxed paper covered with Graham crumbs to cool.
Next time I am going to try cooking them on parchment paper and letting them cool there and break apart after they are cool.