Hard tack should ring like a ceramic tile when you tap on it.
If it doesn't, you didn't make it right.
Ingredients: Flour. Salt. Water (but gets removed during making.)
Bowl. Flower in bowl. Splash in some water and mash up with fork. It should stay dry. More water, more mashing. Mash until it BARELY holds together.
Dump salt over it (kosher, sea, or whatever, not iodized in any case). Mash more. It should be difficult to kneed now. Taste it. If it tastes too salty you are done, if not, add more salt.
Roll out and bake on a cookie sheet spread with more salt and flour. I start at 350 and bake until it gets decently hard, then step down to 250. It may not brown much. Use hardness as a guide for done.
Throw it in some tupperware and wrap in plastic after its cool. Keep in a cool dry place.
It'll keep for years. I have some from 2004 that is as good as it was the day I made it. (Which, is not very good.)
Toss in soups, break off a bit for coffee. Or if you have a lot of water, just put a chunk in your mouth and let it melt. Also good for cracking up and sticking in hot bacon grease, then add a bit of water when it cools.
It is NOT a pleasant food to eat, but is a good way to store wheat starch and protein without keeping the kernels intact.