To test mixture is ready to spread, place a small amount on the back of a dry spoon; let cool. Peel mixture off. If the mixture doesn't peel off easily, microwave for 45 seconds more.
If half of the mixture dries up while you spread the other half, beat it again and microwave for about 1 minute. Check for peeling consistency (see note above). Lumps will be inevitable but the mixture won't go waste.