You don’t discard cards until Recall resolves. If you don’t have X cards in your hand at that time, you discard all the cards in your hand.

You don’t choose which cards in your graveyard you’ll return to your hand until after you discard cards. You choose a card in your graveyard for each card you discarded, then you put all cards chosen this way into your hand at the same time. You may choose to return some or all of the cards you just discarded.

Recall : règles, fonctionnement et interactions (MTG)

Recall is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Discard X cards, then return a card from your graveyard to your hand for each card discarded this way. Exile Recall.

How it works : Recall

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
You don’t discard cards until Recall resolves. If you don’t have X cards in your hand at that time, you discard all the cards in your hand.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
You don’t choose which cards in your graveyard you’ll return to your hand until after you discard cards. You choose a card in your graveyard for each card you discarded, then you put all cards chosen this way into your hand at the same time. You may choose to return some or all of the cards you just discarded.
No other card is named in this ruling.