The top is a bird, the bottom is fire. The bird is being grilled, which was the popular way to cook. So the original meaning of the character is Grill.
The big and small seal scripts for character is
The left one has three birds on the top, the fire on the bottom, grilling three birds at the same time. The right one has only one bird on the top.
Because most of time if not all of the time, the grilling meat is over burnt partially at least the out side. So the meaning transferred to Burnt, many times it means Over Burnt.
The clerical script for the character is
Let's see how the Fire become four dots.
The big seal script of character Fire