Brachot 40 - Serving bread
In general, one should eat the bread right after he said the blessing on it. However, if he interrupts for the needs of the meal, this is considered a necessity, and later he can eat without saying the blessing again. For example, Rav, having broken off a piece, would give pieces to his guests, saying to each "Please take a piece of this bread which has been blessed." Rabbi Yochanan added that if he says, "Bring the salt, please" or "Bring the relish," this is also a necesssity, and not an interrupttion. Rav Sheshet said that even if he says, "Knead food for oxen," that, too, is not an interruption, because one is a supposed to feed his animals before he eats himself, as the Torah said in Shema, " And I will give grass for your animals... and you will eat and be satisfied ."
If one took a fruit and, instead of the proper blessing of "Blessed is the One Who created a fruit of a tree" said the blessing on vegetables, "Who created the fruit of the ground," he has fullfilled his obligation to bless before eating, since, after all, fruit do grow from the ground. The other way around is not true, since vegetables do not grow on trees. If he said a generic blessing "Blessed is the One by Whose word everything was created" on any food, he has also fulfilled his obligation, because his words are true. Nevertheless, one should learn the proper blessing for each food, and in this way he will praise God better.
Art: Francisco De Goya y Lucientes - Still life with fruit, bottles, breads