The timing can vary widely depending on your oven, so if the cake starts looking and smelling done, give it a test and ...

Cool the cakes in the pans for 20 minutes, then invert them onto a rack to let them cool completely. Peel off the parchment paper. In a blender or food processor, pulse the sugar until powdery.

Drain the mandarin segments and place on kitchen paper. On a serving board, carefully cut the cool cake through the middle to give you two large flat rectangles (I like to use a bread knife and ...