It occasionally happens that when one returns home from the synagogue on Friday night, the Hallot are still being warmed up, either in the oven or on the hotplate or "blech." Must the Hallot be placed on the table for Kiddush, or may they be left to continue warming until one is ready to recite "Ha’mosi" over the Halla?
The Gemara in Masechet Pesahim (100) tells that Rabba Bar Rav Huna once visited the home of the Resh Galuta (Exilarch) on Friday night, and a table, with bread on it, was brought before him. Rabba placed a cloth over the table and recited Kiddush. The Gemara provides the Halachic background to Rabba’s actions, citing a Berayta which states that the table should not be brought before a person until after Kiddush, and if it is brought, it should be covered for Kiddush. Tosafot (commentaries by Medieval French and Geman Talmudists) explain that in ancient times, people used small, individual tables, which were set with food and then brought to each person at the meal. The Gemara here instructs that a person’s table should not be brought to him until after Kiddush, and if it is, it should be covered for Kiddush. Tosafot then raise the question of how to reconcile the Gemara’s ruling with a different passage in the Gemara which states that angels escort a person to his home on Friday night and grant him a blessing if they see his table set and his home in order. This would certainly imply that everything should be already be set in place for the meal before Kiddush. Tosafot answer that the tables should be set before Kiddush, but they should not be brought to the people until afterward.
Regardless, Tosafot note that nowadays, when we sit around big tables, and quite obviously we do not have the table brought to us, the table should be set with the Hallot before Kiddush. This is also the clear implication of the Arizal (Rav Yishak Luria of Safed, 1534-1572), in Sha’ar Ha’kavanot, where he describes the procedure one should follow upon returning from the synagogue on Friday night, and mentions that the Hallot should be on the table even before Kiddush. This is, indeed, the prevalent custom, to place the Hallot on the table, covered both on top and on bottom, before Kiddush. (The coverings serve to commemorate the Manna which fell for Beneh Yisrael in the wilderness, which had a protective layer of dew on top and on the bottom.)
It must be noted, however, that this is just a custom, and is certainly not indispensable for fulfilling the Misva of Kiddush. Certainly, if, for whatever reason, the Hallot were not on the table for Kiddush, the Misva has been fulfilled. Furthermore, one does not have to delay Kiddush for this purpose. For example, if one attends a Sebet or is at a hotel, and the bread has not yet been brought to the table, one may recite Kiddush without the bread if he anticipates that by the time everybody finishes washing the bread will be available. And if one would like to keep the bread warming, the best solution is to take two other Hallot or rolls and place them on the table for Kiddush. There is no requirement to use for Ha’mosi the bread that had been on the table for Kiddush.
Summary: It is customary to have the Halla on the table already for Kiddush, but one should not delay the recitation of Kiddush while he waits for the bread (such as at a Sebet, or in a hotel). If one wants the Hallot to continue warming during Kiddush, he may take other rolls or Hallot and place them on the table for Kiddush.