The Rambam (Rav Moshe Maimonides, Spain-Egypt, 1135-1204), in Hilchot Berachot, addresses the case of a person who picked up a glass of beer, and began reciting the Beracha with the intention of reciting "She’ha’kol Niheya Bi’dbaro," as required before drinking beer. However, he mistakenly concluded the Beracha with the words "Boreh Peri Ha’gefen," as though he were drinking wine. Normally, of course, reciting "Boreh Peri Ha’gefen" over beer does not fulfill one’s obligation, and one would then have to recite "She’ha’kol." In this case, however, the Rambam writes that one has, if fact, fulfilled his obligation. Since he recited the critical part of the Beracha – "Baruch Ata Hashem Elokenu Melech Ha’olam" – with the intention of reciting the correct Beracha, this establishes the Beracha as valid, even if in the end he recited the wrong words.
Although the Rambam’s ruling is very novel, it is nevertheless accepted by the Shulhan Aruch (Orah Haim 209:1), and this is, in fact, the Halacha. As long as one recited the words "Baruch Ata Hashem Elokenu Melech Ha’olam" with the intention of reciting the correct Beracha, the Beracha is valid even if in the end he concluded the Beracha incorrectly.
However, the Kaf Ha’haim (Rav Yaakob Haim Sofer, Baghdad-Jerusalem, 1870-1939) adds that preferably, before the person in this case drinks the beer, he should think in his mind the entire Beracha of "She’ha’kol."
Hacham Bension Abba Shaul (Israel, 1924-1998) notes another application of the principle which the Rambam establishes in this ruling. If a person used the restroom after eating, such that he must now recite both "Asher Yasar" and a Beracha Aharona, the Halacha is that he should first recite "Asher Yasar" and only then the Beracha Aharona. If a person at that point recited "Baruch Ata Hashem Elokenu Melech Ha’olam" with the intention to recite the Beracha Aharona, and he then remembered that he is supposed to first recite "Asher Yasar," we might assume that he can then immediately switch and recite "Asher Yasar." Based on the Rambam’s ruling, however, Hacham Bension writes that one may not recite "Asher Yasar" at that point. According to the Rambam, whose position, as we saw, is accepted as Halacha, one’s intention while reciting "Baruch Ata Hashem Elokenu Melech Ha’olam" establishes the nature of the Beracha, and it therefore cannot be changed afterward. Hence, in the case described, the individual should conclude the Beracha Aharona and then recite "Asher Yasar."
Summary: If one began reciting a Beracha intending to recite the proper Beracha, but, for whatever reason, he ended up reciting the wrong Beracha – such if somebody began reciting "She’ha’kol" over water, but he ended up saying "Boreh Peri Ha’gefen" – he has nevertheless fulfilled his obligation. As long as he recited "Baruch Ata Hashem Elokenu Melech Ha’olam" with the correct Beracha in mind, he has fulfilled his requirement and does not then recite the correct Beracha. If a person is required to recite both "Asher Yasar" and a Beracha Aharona, and he begins reciting a Beracha with the intention of reciting the Beracha Aharona, but then realizes that in this case "Asher Yasar" should be recited first, he should continue reciting the Beracha Aharona. Since his intention when he recited "Baruch Ata Hashem Elokenu Melech Ha’olam" was to recite a Beracha Aharona, he should complete that Beracha and then recite "Asher Yasar" afterward.
