Blaze of Glory

You expend all available spell slots, channeling as much energy you can in one attack, causing a massive flaming sphere 20 feet wide to envelope a point you can see within range.  Any creature within the sphere must make a dexterity saving throw, taking fire damage equal to 1d6 per spell slot level expended (1st level spell slots add 1d6, 2nd level spell slots add 2d6, etc) on a failed save, or half as much on a success. A creature with a resistance or immunity to fire damage takes damage as though they did not

Example. A third level wizard with all their spell slots would expend their two 2nd level spell slots for 4d6 plus their three 1st level spell slots for 7d6 damage