What are the dimensions of the cake you are calling a "full sheet"?
I agree with mortega5. I use a flat cookie sheet, the kind with no sides, when I torte most cakes.
I torte the cake, then gently slice the top layer in half (across the width) with a bread/serrated knife. So, I basically take the top layer off in two pieces, fill the cake, then replace the two halves of the top layer. When the cake is iced, it's impossible to tell it's been cut. It's so much easier than trying to lift off a huge, thin layer of cake.
Freezing that top layer works wonders--you can position it perfectly, do a crumb coat and come back and finish after it's thawed. No chance of breakage, and no need to cut.
I always bake sheet cakes on parchment paper. The bottom becomes the top. Leave the paper on until you have filled and placed it back on top. I use a cake board to move it (the paper just gives it extra stability). Peel the paper off and you are ready to ice the cake.
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