To make the strawberry sauce, combine strawberries, sugar and water in a small saucepan. Bring to a simmer over medium heat, then cook on low heat until the mixture looks like a very thin jam and the strawberries are tender (5-10 minutes).
Mix 2 teaspoons cornstarch with 2 teaspoons water in a bowl. Whisk into strawberry sauce and bring to a boil, whisking constantly. As soon as the sauce begins to thicken, remove it from the heat. Allow to cool completely. Once cool, stir in one teaspoon of rosewater (plus more to taste). Keep covered in the refrigerator for up to 1 week.
To make the mascarpone cream, place mascarpone and whipping cream in a large bowl. Using a mixer (I like my hand-held one for this), beat the mascarpone and cream on low speed, just until they mix slightly.
Sprinkle the mixture with powdered sugar and vanilla bean paste, then keep mixing on low speed until it all comes together. You want to see light peaks and a smooth fluffy texture. (Do not over-mix mascarpone as it will curdle.)
To assemble the cups, divide the pound cake among 5 glasses or serving bowls. Top each with equal amounts of strawberry sauce. Lastly, top each with equal amounts of the mascarpone filling. Serve immediately or keep in the refrigerator and eat within 2 days.