The French macaron, by far, has been the most difficult baked good I've ever attempted. It's such a finicky cookie and any slight variance affects its success or failure. At first, I ran into the common macaron issues - bumpy tops, cracked tops, lopsided cookie, no feet, spreading/bursting "feet", blotchy color, etc. After a few batches and some slight adjustment, they started looking perfect with their classic smooth tops and slightly lifted "feet" but it was always hit or miss with the texture. One batch would come out with ideal cake-like centers, another batch would be completely hollow. It drove me absolutely crazy.
After testing numerous recipes, reading countless blogs, watching tons of videos (my husband and I even attended a macaron class in Paris when we went to Europe this past February), I think I can finally say this cookie has been figured out.