Peel and dice the sweet potatoes and cook them in boiling water for about 10 minutes until just tender. Drain thoroughly, return to the saucepan and mash until smooth. Leave to cool.
Lift the bread pan out of the machine and fit the blade. Put the ingredients, except the cheese and tarragon, in the pan, following the order specified in the manual. Add the mashed potatoes with the milk.
Fit the pan into the machine and close the lid. Set to a 750 g (1½ lb) loaf size on the basic white programme. Select your preferred crust setting. Add the cheese and tarragon when the machine beeps.
At the end of the programme lift the pan out of the machine and shake the bread out on to a wire rack to cool.