I've just read a blog post from Amass restaurant. I got very curious about roasting beetroot in coffee grounds as they said in the article. Looking a bit further, I've also found an article by Amass' chef, Matt Orlando, where he gave us a bit more detail on it:
We roast beetroot in the grinds and dry them until they are rock hard. Then we juice some other beets (saving the pulp for kombucha) and reduce this with used tea leaves from the restaurant service. We rehydrate the dried coffee grind-roasted beets in the beet and tea reduction and they end up having a wonderful toffee texture.
Inspired by this, I thought about baking small beetroots (and maybe carrots too) using the salt crust technique, but replacing salt by coffee. I'm thinking about trying using egg whites in one of them, and in the other just burying the beets on the grinds. I'm just a bit afraid that the grinds might burn during the cooking. Anyone has ever tried replacing salt in the crust with something else? I would love some advice from some more seasoned cooks to make this work.