Prepare the syrup (sherbet): Mix 3 cups sugar, 2 cups water, and juice of half a lemon in a pot. Optionally add 2 tablespoons glucose honey or regular honey. Heat on medium, stirring halfway until sugar dissolves. When it boils, stop stirring and simmer for 15 minutes. Remove from heat, add 1 teaspoon vanilla, stir, and let cool completely. The syrup should be heavy and cold.
Prepare the kunafa: Take 500 grams kunafa and let it rest outside if refrigerated to lose coldness. Chop medium threads by hand, knife, or scissors. Mix kunafa with 4 tablespoons powdered sugar evenly. Melt 1 cup ghee and mix thoroughly with the kunafa until all pieces are coated.
Assemble the base layer: Grease a 30 cm tray with ghee, covering inside and sides. Spread two-thirds of the kunafa mixture evenly and press firmly using a smaller flat tray or your hands to close gaps and hold the shape, including the sides to form a border.
Make the cream filling: In a bowl, combine 3 cups milk, 6 tablespoons starch, 1 tablespoon flour, and 1 and 1/4 cups cream. Stir well and cook over medium heat, stirring constantly until it thickens and bubbles. Remove from heat and add 1 teaspoon vanilla. Let the cream cool and thicken before use.
Add cream layer: Pour the cooled cream evenly over the base layer in the tray. The cream will spread to the edges but should be contained by the kunafa border. Let it rest for 15 to 90 minutes depending on room temperature to set.
Add the top kunafa layer: Spread the remaining one-third kunafa mixture evenly over the cream layer. Press lightly to level and connect with the sides. Avoid pressing hard to keep texture.
Bake the kunafa: Preheat oven to 200°C (392°F). Bake the kunafa until the sides are dark brown and separate from the tray. Then turn on the grill to brown the top golden. This process ensures a crunchy golden crust.
Finish and serve: Remove from oven and let rest for 10 minutes. Pour the cold heavy syrup evenly over the hot kunafa. Let it absorb for 15 to 30 minutes, then drain any excess syrup. Serve warm or cooled, optionally with nuts.