Answer : Thin Layer is formed on the side which touches the Tawa (Griddle) first.
The reason is presence of Protein in wheat, and its nature of protein that it solidify when heated.
The wheat dough is made up of individual proteins floating in water, the proteins consisting of long-chain molecules twisted and held in a roughly spherical shape by chemical bonds. As it is heated, these bonds break and the molecules unravel, bonding with other molecules to form a network that traps the water and turns solid.
The side which gets heated first, thin layer solidifies quickly and separates and thus the other side becomes thicker than the side heated first.
