When a person washes his hands in preparation to eat bread, he must recite the Beracha of "Al Netilat Yadayim" before he dries his hands. If one dried his hands and then remembered that he had not recited the Beracha, should he recite the Beracha at that point, or did he miss his chance to recite the Beracha?
The Rema (Rabbi Moshe Isserles, Poland, 1520-1572), in his glosses to the Orah Haim section of the Shulhan Aruch (158:11), rules that one should recite the Beracha in this case. This ruling is based upon the position of the Hagahot Oshri (notes to the Talmud commentary of the Rosh), at the end of the first chapter of Masechet Berachot, that allows one to recite the Beracha over a Misva even after the Misva is performed. The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), however, maintained that one does not recite a Beracha after performing the Misva. According to his view, then, once a person dries his hands, and has thus completed the Misva of Netilat Yadayim, he may no longer recite the Beracha.
The Ben Ish Hai (Parashat Shemini, 7; listen to audio recording for precise citation) applies to this situation the rule of "Safek Berachot Le’hakel," meaning, that one should not recite a Beracha in situations of doubt. Given the uncertainty as to whether the Beracha may be recited after one has dried his hands, the Ben Ish Hai maintains that one should not recite the Beracha in such a case. This is also the position of Hacham Ovadia Yosef, in his work Halichot Olam (vol. 1, p. 317; listen to audio recording for precise citation). Hacham Ovadia emphasizes that one who does recite a Beracha in this case is considered to have recited a Beracha Le’batala (a Beracha in vain). Furthermore, he writes that one should not recite the Beracha even "Toch Kedeh Dibur" – within three seconds – after drying his hands.
This Halacha should impress upon us the importance of ensuring not to begin drying one’s hands until he completed reciting the Beracha of "Al Netilat Yadayim." Besides the fact that one should not perform any activity while reciting a Beracha, there is also the concern that one may complete the drying before completing the Beracha, in which case he would have recited a Beracha Le’batala. Therefore, it is imperative to first recite the Beracha and only then begin drying one’s hands.
Summary: When one washes "Netilat Yadayim" for bread, he must not begin drying his hands until after he completes the recitation of the Beracha. If he did not recite the Beracha until after he dried his hands, he may no longer recite the Beracha.