Tomatoes from the garden make the best salsa which best identifies the adjective phrase and the word it modifies in the sentence

The main function of an adjective is precisely to modify  a noun, often by giving a characteristic to it. There are many different adjective phrases,which are sentences in which one adjective modifies a noun, sometimes using  intensifiers and other features.  In this case, the adjective in its superlative form is the best  and the word it is modifying is salsa, because according to this sentence, the tomatoes from the garden have the particular characteristic of making nog simply good salsa, but the best one, the one with probably the best taste, color, or any other feature.  

the best salsa: modifies make.

in our power to make a world happy - to teach mankind the art of being so - to a character hitherto unknown - and to have, as it were, a new creation intrusted to our hands, are honors that command reflection, and can neither be too highly estimated,