You hurl an erratically twisting and flickering flame at a creature you can see within range. The target must make a Dexterity saving throw. On a failure, it takes 2d10 fire damage and is Burning (PHB p. 362). While the creature is Burning, the damage dealt by its weapon attacks is halved.

Creatures immune to fire damage are immune to this effect.

At Higher Levels. When you cast the spell with a spell slot of 3rd level or higher, the initial damage increases by 1d10 for each slot level above 2nd.