when making rectangular cakes, they seem to bake fine but when I frost them they always end up sloping down...what am I doing wrong? I think I am not using the right technique?

I always ice the top of my cake first and carry the icing over the side. Then I ice my sides, pusing the icing over the top of my cake. Then I drag my slanted spatula from the outside edge to the inside... creating a nice level top. You might have to build up the edge a bit to get it to work.

"they bake up fine". Does this mean your corners are exactly the same height as the center of your cake? If not, then they are not really "baking up fine" or else you need to work on your leveling. If they are the same height, then I'd guess it's something to do with your icing technique. Can you help clarify?

One thing I learned along the way is that I didn't have to ice to the shape of the cake. Meaning, I used to think the icing had to "match" the shape of the cake. Once I learned that I could put extra icing on a low corner to build the corner up to the correct height, it became (as we say in the trade!) "a piece of cake!" I've also since learned that this is a common mistake folks make so I felt better knowing I wasn't the only one!

I have the same problem but it appears to be when I put on the fondant - it seems to weigh down on the corners so they slope. So I try to build up the corners and let the crumb coating firm up well in the fridge. When covered I use my smoothers to form/push the corners in to right shape - but I'm still not happy with my corners....

This happened to me and the advice I was given was my cake was not firm enough so the weight of the icing pulled the corners down.
I know crumb coating and refrigerating first works well.

Corners will not just "pull down" or "slope" unless they are not level with the rest of the cake, which takes me back to thinking its a leveling issue.

If the center of the cake is 2" tall but the corners are 1-7/8" tall, then there is a gap. And gravity is going to work on that gap, pulling the cake down to fill that gap. I dont' care how firm your icing may be, I dont' think icing is strong enough to hold up a cake under the weight of fondant.

if the cake is 2" tall at any and all points .... center, edge, corner, anywhere ..... then a 2" cake, topped with (let's say) 1/4" of filling, topped with another 2" cake, is going to be as squared off as a mason's brick. and just as solid.

I would recheck the cake to see if there is a height issue on the corners.

Check to make sure you're spreading your filling evenly all the way to the edges (or to the dam).

to answer indydebi's question, without using a level and just eyeballing it, it looks even to me until I start stacking and frosting. I think it is my icing technique. This chocolate cake I made (2 11x15 side by side) seemed very moist.

Are you by any chance using wilton pans? If you measure their pans you will find that the bottom is usually smaller then the top by about an inch. They slope slightly outward. I don't know if this is the problem, but it may give you a place to start. For example, if you measure Wilton's square 16 inch pan...it is 16 inches on the bottom of the pan, but it is about 17 inches across the top of the pan. This creates a slight slope. I found this out today when I used these pans for the first time. Not happy about it, but I had no choice at that point but to use them. They were bought specifically by the bride for this cake, because she wanted a square 4 tiered cake and I didn't have any square pans the size she wanted.

I understand exactly what you mean about the corners sloping down. If you have leveled your cake and you have any cake scraps left over, you can lift the corner of the cake with a spatula and put some thin pieces of cake scraps underneath the corners to lift them up. Then when you ice the cake, no one will be able to tell the difference. It has worked for me before.

yes I do love the Wilton pans but never noticed this. Thanks for your input everyone. Pat

I have had this problem also when using Wilton pans, not so with Fat Daddio's. I just "prop" up the corners by using some cake scraps left over from leveling. Just cut and place under the corners. Pieces are usually pretty thin, no one will know!