Prepare the Lemon Filling:

1. In a medium saucepan, whisk together the lemon juice, lemon zest, sugar, egg yolks, and cornstarch.
2. Cook over medium heat, whisking constantly, until the mixture thickens and starts to bubble (about 5-7 minutes).
3. Remove from heat and stir in the butter until smooth.
4. Transfer the lemon filling to a bowl, cover with plastic wrap directly on the surface to prevent a skin from forming, and chill in the refrigerator for about 2 hours.
5. Once cooled, fold in the whipped cream to create a light, mousse-like filling.

Prepare the Charlotte Cake:

1. Lightly dip the ladyfingers in lemon syrup or lemon juice to soften them slightly.
2. Line the sides of a 6-inch springform pan (or any round mold) with the ladyfingers, standing them upright with the sugared side facing out.
3. Line the bottom of the pan with more ladyfingers, trimming as needed to fit.

Assemble the Charlotte Cake:

1. Spoon the lemon filling into the center of the ladyfinger-lined pan, smoothing the top with a spatula.
2. Cover and refrigerate the cake for at least 4 hours, or overnight, to set.

Garnish and Serve:

1. Once set, carefully remove the cake from the springform pan.
2. Garnish with fresh lemon slices and edible flowers for a beautiful finish.
3. Dust with powdered sugar, if desired, for an extra touch of elegance.