Start by baking off the boxed lemon cake in 2 - 8" baking pan, lightly greased and bottom lined with parchment paper. Prepare and bake as per the instructions on the package. Let them cool completely before assembling the charlotte.
1 box Lemon Cake Mix
Prepare the lady fingers by trimming off one of the tips, just enough to get a straight edge. If you made the ladyfingers yourself, this is also where you can make sure they are all the same height, about 4-5 inches.
20 pieces Lady Fingers
Make the lemon syrup by combining the water, sugar, lemon zest and juice, in a small sauce pan. Bring to a simmer, just until the sugar is fully dissolved. Transfer the syrup to a heat proof container and refrigerate until ready to assemble.
½ cup Water, ½ cup Granulated Sugar, 1 piece Lemon
Prepare 450g (1 pound) of the strawberries by hulling and quartering them. These will be for layers of fresh strawberries. Set aside.
450 grams Fresh Strawberries
How to Make the Strawberry Mousse
Prepare the strawberry mousse by first sprinkling the gelatin powder over the water. Set aside until fully congealed.
2 tablespoon Gelatin Powder, 100 grams Water
Pour the whipping cream in a large, clean, bowl. Use a hand mixer to whip it up until peaks start to form. Mix in the sugar for a minute. Set aside in the refrigerator.
Puree the 300g of quartered strawberries by using a high-powered blender or a stick blender. Microwave the set gelatin for 10 seconds, or until just melted. Pour it into the pureed strawberries and blend in to combine.
300 grams Fresh Strawberries
Pour the strawberry mixture into the bowl of whipped cream. Use a hand whisk and/or rubber spatula to fold the two together. Make sure to obtain a smooth texture, while trying to keep as much air as possible into the mixture.
How to Assemble the Charlotte
Place the 9" ring of a springform pan on the cake's serving plate. Cut a strip of parchment paper to line the inside of the ring (side only).
Line up the trimmed lady fingers with the straight end on the bottom, facing them towards the outside. Make sure they fit tightly all around the inside of the ring.
Trim the domed top off of the cooled cakes. Carefully place one of the cakes on the bottom of the springform pan, inside of the lady fingers.
Use a pastry brush to lightly soak the bottom layer of cake. Cover the cake in a single layer of chopped strawberries. Spoon half of the strawberry mousse on top of the strawberries and level it out.
Repeat the previous step by soaking the cake, adding a layer of strawberries, and spooning in the remainder of the strawberry mousse.
Use the back of your spatula to flatten the top of the strawberry mousse. Transfer the assembled charlotte to the refrigerator. Let it set for at least 4 hours or even overnight.
Once the cake has chilled and is fully set, decorate the edge of the charlotte with a border of piped whipping cream. Place halved strawberries in the center for garnish. Keep in the refrigerator until ready to serve.