Conflagrate

You burn a target and make them susceptible to fire. Make a ranged spell attack against the target. On a hit, the target takes 1d6 fire damage and is marked with fiery rune for the duration of the spell. In any round after the one when this spell is cast, a target that takes fire damage from any source takes an additional 1d6 fire damage. This effect can only occur once per round. 

Both instances of this spell's damage increase by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).