Using a serrated knife, trim the sponge down to 6 inches diameter (7 inches if you are using the 8 inch springform pan as your cake mold) and cut in half horizontally to make two thin layers. This will ensure that the sponge layer is not visible when you serve the cake. I'm emphasizing this point because if you look at the picture illustrating this post, you'll see a classic example of "do what I say, not what I do."
Adjust your cake ring to be 7 inches in diameter.
Line the cake ring with an acetate strip. If using an 8 inch springform pan, line with the bottom and sides with several pieces of plastic wrap to ensure easy removal. Place the cake ring on your serving plate, or on a cardboard cake board.
Place the first sponge half in the bottom of the cake ring. Remember, your sponge should be slightly smaller than your cake ring.
Brush with simple syrup.
Hull the strawberries, then slice the strawberries in half, ensuring that all of your strawberries are roughly the same size. Line the perimeter of the cake ring with strawberries, with the cut side facing out. Chop any remaining strawberries into small pieces, leaving 2-3 strawberries for decoration.
Put the creme mousseline in a piping bag fitted with a half inch tip. Pipe thoroughly in between each strawberry, leaving no gaps, then fill in the rest of the sponge cake up to the height of the tallest strawberry, with spirals of creme mousseline, starting at the center and working your way out. Reserve any remaining mousseline cream for decoration.
Scatter the chopped strawberries over the top of the creme mousseline layer.
Brush the simple syrup over the second piece of sponge cake and add it to the top of the creme mousseline. Push it in a little bit, so that you are sure that the creme mousseline is coming up to the top and the sponge cake is hidden by the tops of the strawberries. Brush additional simple syrup over the top, ensuring that the edges, which can be dry, are well saturated with the simple syrup.
Heat of the jam in a small saucepan or in the microwave. Push the jam through a strainer into a small bowl, using the edge of a rubber spatula, ensuring that there are no clumps or seeds. Pour the melted jam over the top of the cake. Chill the assembled cake for at least one hour.