Line the bottom of an oval cake ring mold with cardboard, cutting it to fit. Line the sides of the mold with acetate. Line the inside of the mold with the ladyfinger strip with the flat side facing in.
Cut 2 ovals (5½ by 11 in/14 by 28 cm each) from the chocolate sponge. Place one in the mold and moisten with simple syrup. Spread the white chocolate mousse even