Rif Pesachim 24b {Pesachim 114a-b}

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24b

and the reason for the latter is a good reason, and it is good to do so.

{Pesachim 114a}
Mishna:
They mix for him the first cup.
Bet Shammai say: He blesses on the day and afterwards blesses on the wine.
And Bet Hillel say: He blesses on the wine and afterwards blesses on the day.

They bring before him and he is מטבל {dips/makes use of} the lettuce until {/before} he reaches the aftercourse of the bread {of the later lettuce. or: the breaking of the bread. J: this is a non-trivial statement with a big secret, which we cannot get into here}.

They bring before him matza, lettuce and charoset, and even though charoset is not a mitzvah.
Rabbi Eleazar bar Tzadok says: it is a mitzvah.
And in the {days of the} Temple they would bring before him the actual korban Pesach.

{Pesachim 114b}
Gemara:
They learnt {in a brayta}: Rabbi Yossi says: Even though he dipped with the lettuce, it is a mitzvah to bring before him matzah, lettuce, and charoset and two cooked foods.
What are these two cooked foods?
Rav Huna said: Beet and rice. {even these constitute two dishes}
Rabba would specifically go after beet and rice since it exited the mouth of Rav Huna.
Chizkiya said: Even a fish and the egg {smeared} upon it {are considered two dishes}.
Rav Yosef said: Two types of meat - one in remembrance for the korban Pesach and one as a remembrance for the korban Chagiga.

The roasted one as a remembrance for the korban Pesach