"This rare mushroom has a rich scent. Cook it before eating to temporarily increase your maximum hearts."
A Hearty Truffle is a type of mushroom and material found in Breath of the Wild. This mushroom will restore 2 hearts when eaten raw, but can be increased if Link decides to cook it into a Toasted Hearty Truffle over an open flame. Hearty Truffles can be used in a variety of Recipes, and they have an extra cooking effect of extra hearts. Hearty Truffles can also be used to create Black Dye at the Kochi Dye Shop in Hateno Village.
Hearty Truffles are found sporadically throughout all of Hyrule. Unlike many of the other Mushrooms in the game, there aren't as many locations where they are very densely populated. Instead, while they do appear frequently, they are more spaced out. They can be found regularly in the Lanayru, Akkala, Ridgeland, Tabantha, and Hebra regions, although the y are found in every sing eregion, other than the Great Plateau, Dueling Peaks, and Eldin regions.
A couple areas where there is a small cluster of truffles are the two areas with trees, located directly west and northwest of Zora's Domain in the Upland Zorana. There aren't many trees on these mountains, but in the areas with tress at the higher elevations there are a handful of truffles.
Hyrule Compendium entry of the Hearty Truffle.