In a large saucepan, pour in the heavy whipping cream and heat it over medium heat.
Whisk the cream continuously for 15-20 minutes until it thickens and reaches a custard-like consistency.
In a small bowl, dissolve the cornstarch in milk.
Slowly pour the cornstarch mixture into the thickened cream, whisking constantly to prevent lumps from forming.
Continue to whisk the mixture for an additional 3-4 minutes until it thickens further.
If using, stir in the orange blossom water or rose water.
Remove the saucepan from the heat and transfer the ashta filling to a bowl.
Cover the bowl with plastic wrap, ensuring that the wrap touches the surface of the ashta to prevent a skin from forming.
Refrigerate the ashta to chill and set.