Can anyone help me please…

Can anyone help me please…

I am helping my sister in law get started on her sourdough journey.  She has made yeasted breads over the years successfully. This is the second time (her second sourdough bake) that she has had this result – almost white top.  

She is baking in an enamelled roasting dish , but using a loaf tin.  Baking using fan (Bosch electric oven so 4D hot air setting)  at 235°C for 10 minutes after cold over night retard. Then 15-30 minutes without lid.  

I don’t know what to suggest as I have never had this problem.  I have suggested her next bake could be free form to see if it is the loaf tin causing the problem.

Any suggestions gratefully received

Leslie

PS Photo is too large to upload so sides and bottom are golden brown but top virtually white. There was some oven spring and crumb is close not particularly open.  It is approx 45% wholewheat.