I was curious if anyone else has had a issue with macarons having a concave bottom when using a silpat. Ive tried playing with time and temp but still have the issue. Its rather strange, they have perfect feet but no base at all. Some of the shells will have a base, but its usually 2 or 3 out of 30. I use the french method and my ratios are 120g egg whites / 125g Almond meal / 200g confectioners sugar and 6 tbs granulated sugar added to the whites. I dont double pan when using a silpat and bake them at 320 for 15 minutes.