http://skafferiet.no/receipes/item/56-skafferiets-knekkebrod#sigProId3345afac61
50 gr yeast
5 dl lukewarm water
1 1/2 teaspoon salt
1,1 liter rye flour
1 dl white flour
salt flakes
Dissolve the yeast in a bowl with the lukewarm water. Then mix in the salt and the flour. Use a kitchen machine and knead the dough quite heavily. Have a little rye flour on top of the dough, cover it and leave it in the fridge for about 12 hours.
Knead the dough and cut it into 20 pieces. Put a lot of flour on the baking table and roll each piece with a rolling pin. The size should be like a small plate. Don´t use too much power, roll light and easy. After this I change my rolling pin to an old one with a small square pattern on it, to have a nice pattern on the crisp bread. You can probably buy something similar. If not, continue rolling with the traditional one until the size is like a dinner plate. Put the thin dough carefully on a baking sheet covered with baking paper. Have some salt flakes over it and fry in the ovven on 250 gr C (482 gr F) for about 12-15 minutes.