Read step one: “Preheat the oven to 350 Fahrenheit, line 2 6-inch baking pans (or 1 9-inch) with parchment paper on the bottom only. Don’t grease the sides. Set aside.”

Yes on both counts!

Unfortunately that 1x,2x,3x feature is applied across all recipes on my site automatically but does not mean all recipes can be multiplied–which is why you didn’t find any additional instructions for making it larger. I just can’t turn it off for baking recipes. This is definitely not a cake to make in a large multiplied version. As with any baked item, the recipe can go very wrong if multiplied. It’s easy to make casseroles or other savory dishes by doubling or tripling but not this one.

I’ve never done it with berries in the cake. It will make wet pockets but I would put them in the batter once I’d transferred it to the baking pan to reduce deflating it.