French Macarons

There are so many variables with macarons. Could be that you beat the egg whites too stiff or not stiff enough, there was a trace of grease in your bowl (I always wipe my bowl with a vinegar-soaked paper towel before beating egg whites. It's insurance.), the humidity was too high, your almond flour wasn't fine enough, etc. Did you let them "set" on the counter at all before baking?

Thats so good to know, I am also going to be attempting them for the first time. I have seen oven temps ranging from 275-300 I think it would be prudent to check the oven temp with an oven thermometer before baking.

Macarons can be tricky. It's possible they were a little underbaked. It may be that your oven runs a little hot so the outside of the macaron appeared done but the inside hadn't set yet and it collapsed as it cooled. Try baking at a lower temperature for a longer time.

I am sorry about your macarons, I am going to be making them for the first time very soon and have been watching video's and preparing myself, it's a little intimidating. First thing that comes to mind is that maybe they had too many air bubbles in the batter. One of the video's that I watched showed the chef after adding the egg whites to the flour mixture literally flattening the batter gently along the sides of the bowl to remove some of the air bubbles, taking it further she slammed the sheet pan 3 times on the counter to remove even more air bubbles. I have also heard that temperature and humidity are a factor in how they turn out. I am not a macaron expert but have been doing some research before making them and thought maybe this could be a factor in your fallen shells.

Without actually witnessing your process it's difficult to say. Was your bowl spotlessly clean when you made the marangue? Perhaps your eggs were not as fresh as they need to be for this type of recipe. Macaroons can be tricky.