What compound can make crunchy biscuits?
Your comment update suggests that you might be melting the butter ... don't.  Melted butter will make for a softer, chewy cookie..
I don't know if there are episodes of Good Eats available legally online, but there are transcripts of them ... you want episode 'Three Chips for Sister Martha' in which he discusses how some slight changes to a cookie recipe will make for dramatically different cookies:

Back to butter. But this time we're going to melt it.
...
The water from the melted butter will combine during agitation with the higher protein of the bread flour therefore producing gluten ... which is chewy.

You likely want to look at what he did for 'The Thin' variant, which is the only crispy variant in the episode ... but that's not to say that you can't make thick crunchy cookies.  (one of my favorites is LU's Bastogne cookies;  speculaas also comes out crunchy even when fairly thick)  Unfortunately, the recipe from that episode focused on thin (with the side-effect of crispy/crunchy), rather than mentioning what could be done to make it crunchy without making it thin.