I've already baked good macarons, but sometimes, for some reason, they do this and I really don't know what could be the problem.
here is my oven description in case you think that's the problem (but as i said, it does bake them well most of the time)
It's a convection oven with two main options "true fan cooking" (just fan) and "moist fan baking" (fan + sides) i've tried both and they both give about the same results, with both modes having a chance or turning like this. I do preheat lower than what most recipes say, because otherwise they overcook: 135°C (or 130 for raspberry macarons)
preheat: 20 minutes
bake: 15 minutes
I do italian macaronage, and follow the recipe from cupcakeJemma
by yoyuanuan