We recently moved into a new house and we've been having issues with the oven. It runs about 25 degrees higher than what you set it on. We bought a thermometer and now adjust the temperature accordingly. Don't have any real issues now, except for cookies.
My cookies come out flat as a pancake and burn on the edges, even if the temperatur is lower than suggested and the cookies are taken out early from the oven. I have replaced all my dry ingredients, so we're working with as fresh as possible. I live in eastern Canada, so altitude is not an issue. Maybe humidity? I have tried baking the cookies on a silpat on a heavy baking sheet, and without the silpat on a thin baking sheet, all with the same results. I tried chocolate chip cookies, and peanut butter cookies.
The strange thing is that I have no problems with cakes or muffins. What gives with my cookies??