Baking – Where should heat comes from when baking brownies

You're baking using a convection fan. This generally won't work unless the cake recipe is calibrated for it; you'll end up with a cake which is brown on the outside and raw in the middle (as you did). It's remotely possible that a combination of lowering the temperature and convection would be successful, but I don't have a formula for you.

Suggestions:

If the issue with top heat is that the cake is burning on top before the bottom is done, I would suggest placing a rack above the one the cake sits on, and a cookie sheet on that rack. This will protect the top of the cake from the radiant heat of the element, causing it to cook only from reflected heat off the sides of the oven. This may, however, increase cooking times somewhat so make sure to check cake doneness with a skewer.

Or: Add a baking stone on the rack holding the cake as well (under it), and preheat the stone for 30 min before baking the cake. This will give it some heat from the bottom.

Or: both of the above.

Or: get a new oven. They make fairly nice countertop ovens now which have a bottom baking element.

Some convection ovens have the ability to turn off the fan -- if yours has one, that would be recommended.

One of the big issues is that the cooking time changes based on the surface area of the item being cooked -- so if you have a thin cake, such as a jelly roll (baked thin, then rolled up), your cooking time will be dramatically reduced ... but it doesn't help with large cakes -- you'll just end up with the top browing faster than the middle sets.

In general, the recommendation for convection ovens is to lower the temperature by about 25F / 15C (some newer ones with digital controls will do this automatically), but some people report problems with cakes being overly dense; I've heard different theories (eg, bernoulli effect lowering the pressure in the oven, causing the air bubbles to come out of the batter). Adding a tight covering of aluminium foil might help this, but it will cause other issues (eg, steaming the top).

Another recommendation I've seen for baking in a convection oven is to make sure that your oven has had sufficient time to pre-heat, then when putting in your baked goods, turn the oven off, and leave if off for 3-5 minutes before turning it back on. (this is typically to solve problems with baked goods appearing lopsided, as the fan's blowing so hard it's moving the batter around significantly).