In a small bowl, dissolve the yeast in warm water. Let it sit for about 5 minutes until frothy.
In a large bowl, combine the rye flour, all-purpose flour, salt, and sugar or honey.
Add the buttermilk, molasses (if using), and the yeast mixture to the dry ingredients. Mix until a dough forms.
Turn the dough onto a lightly floured surface and knead for about 5 minutes, or until smooth and elastic.
Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm place for about 1-1.5 hours, or until doubled in size.
Punch down the dough and shape it into a loaf. Place it into a greased loaf pan or shape it into a round loaf and place it on a baking sheet.
Cover and let rise again for about 30 minutes, or until puffy.
Preheat your oven to 375째F (190째C).
Bake the bread in the preheated oven for about 30-40 minutes, or until the loaf sounds hollow when tapped on the bottom and is a deep brown color.
Allow the Ruisleip채 to cool on a wire rack before slicing.
Enjoy your meal!