You want the strawberries to sit flat.  So if they are a little wobbly with the stems left on, cut the green stems off the strawberries so they will stand upright when placed on your serving tray.

 With a small sharp knife, cut an "X" in each strawberry, cutting almost to the bottom of each strawberry.  (The cut should be such that the strawberry will open up but not fall apart.) Gently, with your fingertips, spread each strawberry apart to make "petals".  Set aside while you make the cream filling.

In a medium sized bowl, whip the mascarpone cheese and whipping cream until soft peaks form.  Add the sugar and vanilla and continue to whip until stiff peaks form. 

Spoon the cream into a pastry bag fitted with a large open star tip.  Pipe the cream into the strawberries.  If not serving immediately, cover, and place in the refrigerator until serving time. 

Mascarpone pronounced mas-kahr-POH-nay is a soft unripened cheese that belongs to the cream cheese family. It comes from Switzerland and Italy and is a thick, buttery-rich, sweet and velvety, ivory-colored cheese produced from cow's milk that has the texture of clotted or sour cream.  It's delicate and mild flavor is great with fresh fruit and is probably best known for its use in Tiramisu.  Produced mainly in the fall and winter it is sold in plastic 8 ounce tubs and can be found in specialty food stores and in the deli section of some grocery stores.