I really must be the world's worst baker 
First instruction of clementine cake recipe says put clementines in a pan and boil for 2 hours. Doesn't say anything about whether to peel them or not so I peel them.
Second instruction - blend clementines, skin, pith and all 
Ds has suggested chucking the peel in the pan or option 2 is eat 5 clementines and chuck in the 4 remaining unpeeled clementines.