What is the rationale of making Kiddush at night if one only has sufficient wine for one cup at night, surely at night (Friday) one can make Kiddush on pas (challoh) ?
Sholem, UK
The Mishna Brura writes (271:8)that since Kiddush at night is D'Orayso and in the day it is only D'Rabanan, when one only has one cup he should make Kiddush at night even though during the day he will be left without wine, because when a person has wine he cannot make Kiddush on bread. Apparently it is more important to fulfill the D'Orayso obligation in the best possible manner than to fulfil the D'Rabbanan obligation in the day.
There is also the opinion of Rabbeinu Tam that one cannot make Kiddush on bread and the Rema paskens that if a person has wine he cannot make kiddush on bread in accordance with Rabbeinu Tam. Even though the Biur Halacha says that if a person finds wine repugnant he may make on bread in accordance with the more lenient Rishonim, this is not the case when one has one cup and therefore one should make on the wine at night to fulfill the Dorayso obligation.
Yoel Domb
The BIUR HALACHA IN 171,3 says that if one likes bread better that wine, then he should kiddush on wine.
I presume you mean kiddush on bread, the opinion of the Biur Halacha is that one should buy bread and the requirements for the meal if indeed he likes bread more than wine and should rely on the lenient opinions that one can make kiddush on bread. However if he does like wine as well he should take wine in order to fulfill the D'orayso obligation with wine which is the preferable method.
Yoel Domb