Due to doubt in the correct bracha, the author recommends to separate a piece of the biscuit and to say Borei Minei Mezonos on it before making a Shehakol Niyeh Bedvoro and eating the Krembo.
Generally, a proper shiur of the biscuit is not eaten, so say Borei Nefashos if a proper shiur of the Krembo was eaten.
Source: Sefer Sharei Haberacha (page 685)