Belarusian rye breads are best tasting breads in eastern Slavia in my biased opinion. I have not tried Lithuanian rye breads; their breads may taste as good as Belarusian given similar ingredients and baking techniques are used in Lithuanian bread-making.
The Naračanski chlieb is probably the best known rye-bread out of Belarus. The bread is baked commercially based on a traditional recipe. It’s made of scalded dough with 70% of rye flour and 30 whole grain wheat flour. It’s called scalded because boiling water is added in flour. In adding boiling water into flour starch gelatinisation occurs, whereby it is easier for enzymes to convert starch into sugars. Also, cramb becomes softer if scalded dough is used. There are malt, a certain leavening agent, certain types of flour grinds, molasses, anis , caraway seeds and other ingredients used in bread-making. It may take 2-3 days to complete baking process as no yeast is used.
The Jubilee rye-bread is also based on traditional Belarusian recipe . Traditionally, the bread was baked on Sweet Flag plant (Acurus). Commercially, it’s baked on maples leaves. The process of baking this bread is even more complex than that of the Naračanski which I am not going to desribe. It contains 87% of rye flour.