What is the delicious brown layer that appears when you fry or bake apples, plums, apricots, etc.?
This is a combination of the two: caramelization and Mallard reaction.

Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They both are promoted by heating, but the Maillard reaction involves amino acids, as discussed above, whereas caramelization is simply the pyrolysis of certain sugars.

Mallard Reaction – Wikipedia

Caramelization – Wikipedia