Prepare Strawberry Filling: Place sliced fresh strawberries in a saucepan over medium heat. Add granulated sugar and lemon juice, stirring until juices are released, about 5 minutes. Mix cornstarch with water to create a slurry, pour into the saucepan, and cook for another 2-3 minutes until thickened. Let cool completely.

Make Lemon Cake Batter: Preheat oven to 350°F (175°C) and grease two 9-inch round cake pans. Whisk flour, baking powder, baking soda, and salt in a bowl. In another bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, then vanilla, buttermilk, and lemon juice until smooth.

Combine Wet and Dry Ingredients: Gradually add dry mixture to creamed butter, alternating with lemon zest. Mix gently until just incorporated. Pour batter into prepared pans, smoothing the top.

Bake the Cake: Bake for 30-35 minutes or until a toothpick comes out clean. Cool in pans for 10 minutes before transferring to a wire rack.

Prepare Cream Cheese Frosting: Beat cream cheese and butter until creamy. Gradually add powdered sugar, then lemon juice and zest until fluffy. Set aside.

Assemble the Cake Layers: Level the cake layers. Place one layer on a platter, spread frosting, add strawberry filling, and top with the second layer. Frost the entire cake.

Garnish and Serve: Decorate with lemon slices and edible flowers. Chill for at least 30 minutes before slicing.