On Shabbos when we wash hands for Hamotzi, do we need to say the Bracha Hamotzi or just say Amen to Baal Habayis? Do we have to say Amen or is it an Hefsek since we have already washed?
According to Halacha it is sufficient to respond Amen to the Bracha of the Baal Habayis and there is no need to say your own Hamotzi. Nonetheless, many have the custom that everybody says their own Hamotzi.
Regardless, Amen must be said, and it is not a Hefsek, even if you are making your own Hamotzi.
For a discussion about this custom, see מראי מקומות in Halacha2go.com #607.
For the rules of Hefsek after washing, see Halacha2go.com #593.
See also Halacha2go.com #818 at the end.