This weekend I made two separate sets of what the recipe I have calls macaroons (they don't look like the little shiny spheres I've more recently seen called macaroons, but they taste great). The first batch, made early one morning, came out exactly as I expected them to, after a little experimentation with timings. 13 minutes at 180C made smooth, round, slightly risen and golden almond delicacies... Unfortunately, there are no specimens remaining for photographic proof.
The second batch, made in an afternoon's distraction, contained exactly the same ingredients (2 egg whites, 225g sugar, 175g ground almond), made in the same bowl, and was baked on the same tray, in the same oven, for 13 minutes at 180C. They tasted delicious, but the mix was much wetter, and the resulting biscuits are less smooth, and spread more on the baking tray, though some did rise slightly too. The only difference I can think of? I whisked the egg whites for slightly longer and slightly more vigorously the second time around! Note to self: the smallest change can make a difference.