Make pancake batter by combining all-purpose flour, fine semolina, and whole milk in a bowl. Mix until just combined to avoid overmixing. Let batter rest for 45 minutes.
For syrup: In a saucepan, combine ½ cup sugar and ½ cup water. Bring to a boil, add 2 tbsp lemon juice, then simmer 8-10 minutes until thickened. Remove from heat, stir in 1 tbsp rose water, and cool completely.
For ashta filling: In a saucepan, whisk 1 cup whole milk, ¼ cup cornstarch, ½ cup sugar, and 1 tbsp vanilla extract until smooth. Cook over medium heat, stirring constantly, until thickened. Remove from heat, stir in ¼ cup heavy cream if using. Cool the filling, then cover the surface with plastic wrap to prevent a skin.
Preheat a non-stick pan over medium-low heat. Pour a small amount of batter into the pan to form a round shape. Let cook 90 seconds before gently opening the pancake with a spatula to create a pocket. Fill with warm ashta mixture, then fold the pancake over itself and flatten slightly.
Repeat the process and arrange warm qatayef in a serving dish. Drizzle the cooled syrup over the stuffed pancakes. Sprinkle with crushed nuts if desired. Serve immediately.