Peel and cut sweet potato into small even-sized pieces. Cover with water in a medium saucepan and bring to the boil. Reduce to a medium heat and cook until soft, around 10-15 minutes. Drain well and mash.
Combine yeast, sugar, and warm water in a medium mixing bowl. Leave somewhere warm for about 10 minutes until frothy.
In a large mixing bowl, combine flours, salt and rosemary.
Add oil and mashed sweet potato to yeast mixture. Add this mixture to the dry ingredients and mix well to form a dough. More flour may be needed if the mixture is too wet.
Knead the dough on a floured surface for 10 minutes, adding extra flour when needed. The dough should become soft and elastic.
Place kneaded dough in a lightly oiled bowl, cover with a clean tea towel, and leave to rise in a warm place for 30 minutes. It needs to double in size. I turn my oven on low. leaving the door open and place the bowl on the stove top to provide the temperature needed for the dough to rise.
Line an oven tray with non-stick baking paper. Cut dough in half and shape into 2 loaves. Place these on the lined oven tray and cut a few 1cm-thick slashes on top of the loaves with a knife. Leave to rise for another 20 minutes or so.
Preheat the oven to 200°C Bake.
Bake the loaves for about 25-30 minutes or until a crust has formed and the base is firm and sounds hollowed when tapped with the back of a knife.
Remove from oven and cool before slicing.
Serving Size 1 slice