This is from Heidi Swanson's Super Natural Every Day. I didn't have buttermilk so I used yoghurt. This is a very quick loaf because there's no yeast.
2 1/3 c rye flour
1 3/4 c all-purpose flour
1 3/4 tsp baking soda
1 1/4 tsp salt
2 c buttermilk, plus more for brushing

Preheat oven to 205C and put oven rack in middle of the oven. Sift dry ingredients into a bowl, make a well in the middle and pour in buttermilk. Mix until it just comes together in a dough. Turn out onto a floured surface and knead for 30 seconds or so until the dough comes together in a smooth ball. 
Place ball on lightly floured baking sheet. Brush all over with buttermilk and sprinkle with flour. Slice four deep slashes across the top of the dough in a cross shape, about 2/3 of the way through.
Bake for 30 min, then quickly move the rack and bread up a level so the bread gets toasted on top. Try not to let too much hot air out of the oven. Bake for another 20 mins or until a hard crust forms and the loaf is baked through. It will sound hollow when you knock on the bottom.
Cool on a wire rack.
Best eaten within a couple of days. Then I made big chunky croutons with the remainder (cut into squares, drizzled on olive oil and baked in the oven till crispy). Or you could make breadcrumbs.