Brocho before eating the cake: Borei Minei Mezonos
Brocho before eating the ice cream: Generally, Shehakol Niyeh Bedvoro as well. However, if it is eaten to enhance the flavor of the cake (like if it is a very thin layer), no Brocho is required on the ice cream. If one is in doubt, recite Shehakol Niyeh Bedvoro on the ice cream and then recite Borei Minei Mezonos on the cake (i.e. switch the order).
If one is Koveah Seduah on this item, only Hamotzi Lechem Min Ha'aretz and Bentching are required. (i.e. if one is Koveah Seduah, those are the Brochos that are required no matter what the ice cream's purpose is)
Source: The Laws of B'rachos (pages 223, 370)