Many ashta recipes leave out the sugar because the cream is so often served in pastry that includes a topping of simple syrup. I think at least a little sugar is key in the flavor of this traditional Lebanese milk pudding. Serve it with fruit or use the ashta as a filling for knafeh and other desserts.
In a medium saucepan, combine 6 cups of the milk with the vinegar and heat over medium high heat.
Stir the milk until it is steaming and the whey and cream separate. This will happen swiftly.
Place a strainer over a bowl. Turn off the heat and use a slotted spoon to remove the clotted cream to the strainer. Discard the whey left in the saucepan.
In another medium saucepan (or rinse the last one out), whisk the remaining 2 cups of milk with the cornstarch and sugar.
Cook the pudding over medium heat, whisking constantly until it thickens, about 5 minutes.
Remove the cream from the heat. Add the strained clotted cream and flower waters, whisking until fairly smooth. Use an immersion blender or other blender to smooth the cream.
In a bowl, place plastic wrap directly onto the surface of the cream to prevent a skin from forming. Chill for at least one hour and up to one week before serving.
Before serving, blend the cream again. Arrange the fruit in small bowls and top with a dollop of the ashta. Sprinkle with ground pistachios and serve immediately.