Welcome to the Cake Decorators Q&A

Hi I’ve been sucessfully baking Mrs Jones’ vanilla sponge for many months, but just recently it isn’t rising in the middle. I am using the same ingredients and tins and have checked the oven temperature with a thermometer. I’m at a loss now as to what I’m doing wrong. Any help gratefully received.

Hello Dawn Pledge

You’ve never had a problem with the recipe before so it’s pretty obvious that it’s not your baking!
Just a couple of things which may be going one:

If your thermometer is getting on a bit might be worth buying a new one. Thermometers expand and contract in the oven and after a few months of constant use can give inaccurate readings.
This really sounds like the oven temp to me but other things like damp leavening or flour would prevent cakes rising properly. Over greasing and flouring the cake tins would make the sides bake more quickly than the centre and making the cake collapse. Sometimes for no reason at all a trusted recipe will just suddenly decide not to work in the same oven it has been baked in many times!
Try again Dawn with a new thermometer, it would be a shame to abandon the recipe, it really is a nice one.