I've been working on perfecting a brownie recipe for quite a bit now and finally got it down - the right pan size, the right proportions, the right baking time in my oven. I made it a few times and it consistently came out well!

Today, I tried to make a red velvet brownie. I made the batter as usual, adding red food coloring and white chocolate chips. I did a layer of the batter, a layer of cookies and cream bars, another layer of batter, and topped it wit Oreos. I baked it for the time I always have and it came out raw in the middle, even after leaving it for about 29 mins (I know they continue to bake after they come out of the oven).

I'm sort of new to baking but can someone explain why this happened? Is it because of the cookies and cream bar layer? Do I simply bake longer or should I power the temp and bake longer? For reference, I have a gas oven. Thank you!