Carrot cake with frosting of mascarpone and orange

I made this for my Mum's birthday as she is a fan of carrot cake, but it went down well even with those members of my family who aren't. Nice and light, probably due to the last-minute folding in of beaten egg-white, which makes it a bit fiddlier than some carrot cake recipes but it does pay off. I find the cream cheese icing on carrot cakes can be a bit cloying so I made 2/3 of the frosting and used it to fill and top the cake only - didn't cover the sides.