If using a knife, lightly score the cake evenly around the circumference of the layer and then slice all the way through. Or the cake can be marked with toothpicks. Insert toothpicks into the cake at intervals, making sure they are all placed exactly midway around the circumference, then slice at the toothpicks. Brush away and discard crumbs. For tidier decorating, freeze layers overnight.
Frozen layers are easier to handle and generally free of crumbs.
For filling, first pipe a ring of prepared icing around the top edge of the bottom layer with a No. 12 round tip. This ring prevents the filling from squirting out between layers. Inside the ring, spread a layer of pudding, preserves, fruit curds or pie filling. Fillings can be made or purchased and should be spread no higher than the well made by the icing. When the whole cake has been iced, finish by evening sides and smoothing the top until sides are straight and top is flat.