I have tested two different brands of pretzels (Trader Joe's and Whole Food's 365) and two different shapes (the typical twists and the stick pretzels). I have found that they can vary in terms of how much butter they will need. If your pretzel crumbs feel really dry, add in more butter. And to the contrary, if they feel too wet to form into a crust, add in more pretzel crumbs to balance out the mixture. It should be the consistency of wet sand, and easy to form into a crust.