Not a new concept, but nice nonetheless
You give us 4 slices and tell us not to go below 2 slices, which means we can use 2 slices max.
Why not just give us 2 slices ?
Viewing post in S.C.D. - Spirit Cake Delivery jam comments
At first, different levels would have different requirements and you would be able to get more slices along the way. Also, the levels would have different routes that you could go and there would be multiple parts where you wouldn't be forced to use the cake if you were skilled enough, so it would have some elements of managing these resources while not using all the slices.
In the end I overestimated my level design capabilities and it ended up not having these elements =)