Why is my toffee grainy in cracker-toffee "Crack"? I have made this recipe to good results (creamy, chewy toffee), and more often, to disappointing results texturally (grainy toffee). 

It is :
1 cup butter
1 cup brown sugar

Cook for 2-3 minutes stirring constantly. pour over saltine crackers on a greased foil lined cookie sheet, and bake at 350 for 10 minutes. top with chocolate chips, spread when melted. 

I have read many versions of this recipe with more cooking time and more baking time (and people with burnt results from the longer baking). I know traditional toffee made with white sugar is not to be stirred, the whole pastry brush thing, but this one is different. I wonder if I am not cooking the toffee on the stove long enough, eg to soft ball stage. 

Also wonder if using ordinary brown sugar is ok.

It tastes good no matter the texture, but I would like to be able to nail it more consistently re the texture! Thanks.
Brown sugar can be used to good effect in candy making.

With the texture issue, something is crystallizing the sugar. Try using your ingredients with the more classic method.