They've fallen and they can't get up
I've been cooking for almost 50 years and still have the same problem. Whenever I cook muffins, cupcakes, cookies -- whatever -- they rise nicely while they're cooking, but by the time I take them out of the oven they're flat as a pancake. That just happened this afternoon with vanilla cupcakes, my grandson's favorite.
I have a gas oven. I turn the pan half-way through baking so they'll bake evenly. I followed the directions exactly. The recipe was for 12 cupcakes, and that's what I made. I'm so frustrated!
I'd appreciate any advice.
The first thought that flashed through my mind is where you live... sounds like something that would happen at high elevations such as Denver, CO. I would say that you may have consistently had dead baking powder, but if it's outdated you won't even get the initial rise.
Buy a fresh tin of baking powder and see if that helps.
You can also add a little extra acidity (lemon juice or buttermilk) to boost the acid/bicarbonate reaction for more fluffiness.
Overmixing the batter will also flatten a muffin.
Last resort, try playing some uplifting music for encouragement.
Check out baking911.com. It's a terrific resource for all sorts of baking info, including many "troubleshooting" pointers. It specifically addresses how to remedy flat muffins, cookies, etc. One really useful tip is not to over-cream fats and sugar - doing so will soften the butter and reduce its ability to hold air. I used to have problems with flat cookies, haven't had them since learning this.
Maybe you're rotating the pans before the batter is set, and the agitation is causing things to collapse. It takes time for the pan and the batter to warm from room temperature to where egg proteins and flour starches begin to set, so halfway through baking time isn't really halfway done. I'd say two-thirds through baking time is closer to halfway done. If suggested baking time for a cake is 30 minutes, rotate it at 20 minutes instead of 15, or if baking time is an hour, at 40 instead of 30 minutes.
Just a theory, hope it helps.
I had the same problem a couple years ago in a previous apartment. It turned out that my oven wasn't heating consistently. You might want to get an oven thermometer.