The sorcerer ability Twin Spell (PH 102) reads:
When you cast a spell that targets only one creature and doesn't have a range of self, you can spend a number of sorcery points equal to the spell's level to target a second creature in range with the same spell
How many sorcerer points do I have to spend when casting a low level spell with a higher level slot?
For example, I cast Ray of Sickness (a 1st level spell) using a 3rd level slot. Would I spend 1 sorcerer point or 3?