Prepare the strawberry syrup: In a food processor or blender, combine half of your fresh strawberries with the strawberry jam and a splash of water. Blend until smooth.
Take the rest of your fresh strawberries and dice them into small, bite-sized pieces.
In a large mixing bowl, beat the cold heavy cream and powdered sugar together until soft peaks form. Gently fold in the chilled mascarpone cheese until thick and smooth.
Working quickly, dip each ladyfinger into the strawberry syrup. Break the cookie in half to fit the cups.
Add a spoonful of mascarpone cream over the soaked ladyfingers. Top with diced fresh strawberries. Repeat until full.
Cover the assembled cups tightly with plastic wrap and refrigerate for at least 4 hours, or preferably overnight. Garnish with a fresh strawberry half before serving.