Peel and cut sweet potatoes into chunks. Steam for about 10-15 minutes until soft and mashable.

In a large bowl, add the steamed sweet potates, butter/oil and salt. Mash well with a fork.

Add the rye flour, bread flour and yeast to the bowl. Pour over about 100 ml water and mix with your hands. If it's still a little dry and crumbly, add more water until the dough is moist.

Squeeze and knead the dough together with your hands until it's not longer floury. Remove to a floured working surface.

Knead the dough until smooth, about 10-15 minutes. It will be a little 'grainier' and tough than regular bread dough because of the sweet potatoes.

If using sesame seeds, put them into a large bowl and then add the kneaded dough to the bowl. Knead the dough in the bowl until the sesame seeds are worked in.

After 9 hours the dough will be about doubled! Dived into 8 equal pieces.

Form each piece into a round bread roll by folding over the edges to the center and pressing the folds to seal. The other side should be nice and round & smooth.

Dust each roll with rye flour. I put some rye flour in a small bowl and then roll the rolls around in it.

Arrange the dusted rolls on a baking sheet and lightly cover with a tea towel. Let rise for 45 minutes to 1 hour. Meanwhile preheat the oven to 230°C/450°F (if possible, prepare to bake with steam too)

Right before putting in the oven, make a cut across the center of each roll. Put in the oven, and bake 230°C/450°F with steam for 10 minutes. Then release the steam, lower temperature to 200°C/400°F and bake for another 10 minutes [Total baking time = 20 minutes]

Remove from oven and let cool on a rack. Enjoy!