You create a swirling ball of flames and fling it at one creature within range.  Make a ranged spell attack against the target.  The target takes 3d10 fire damage on a hit, or 1d10 on a miss.  Hit or miss, the ball then explodes.  The target and each creature within 15 feet of the point where the flames exploded must make a Dexterity saving throw, taking 6d6 fire damage on a failure or half as much on a success.

At Higher Levels.  When you cast this spell using a spell slot of 4th level or higher, the area damage increases by 1d6 for each slot level above 3rd.