Well, kangaroota, since you have been specific about your question, and said all other considerations can be ignored, the least amount of fuel you can consume is clearly "none".
Calculate the engine-out glide angle for your chosen aircraft. Project that glide angle backwards to the point where it intersects your route at cruising altitude, which we will call Top Of Descent. When you reach TOD, shut down all the engines. You are now assured of using the minimum possible fuel from TOD to the airport. Subject to traffic you are not actually assured of reaching the airport but that, as you say, doesn't matter for the purpose of this exercise.
But slightly more seriously, this technique works quite well for jet aircraft, because instead of shutdown they can select flight idle and broadly speaking follow the instructions given above. And the larger transport types, when it is offered to them, do sometimes actually follow a profile close to that ideal.
The calculation for a turboprop is less obvious, because for the "ideal" profile with zero fuel consumption, you'd really need to feather the props when you shut down the engines. On the assumption that reaching the airport with a high degree of certainty DOES matter for the purpose of this exercise, and you want to keep the propellors going round, you've got a drag versus fuel consumption problem to solve. You'll need to keep the engines spooled up in order to keep driving the propellors, so you are not really at idle. So you would actually need a quite in-depth understanding of the propellor drag curve versus fuel burn to know where the "sweet spot" was for the nearest equivalent of the feathered-prop glide approach.
But to go back to my original answer, and to generalise, all aircraft fly faster than their optimum speed almost all the time. So any time you want to save fuel, slow down. Just remember that by slowing down you may be saving fuel, but you might not be saving money.