To separate the two liquids that have formed a solution, the best method among the options provided would be:
heating the liquids and letting one boil away first.
This process relies on the different boiling points of the liquids. By heating the mixture, you can selectively evaporate one of the liquids, which can then be condensed and collected, effectively separating it from the other liquid.
The other options, such as filtering, waiting for separation, or using a spoon, would not be effective in separating the two liquids if they have formed a homogenous solution.