Dessert: Strawberry-Blueberry Napoleons

Ingredients

24 9x14-inch sheets fresh or thawed frozen phyllo pastry (about 3/4 pound)
6 tablespoons (3/4 stick) unsalted butter, melted
16 teaspoons plus 1/2 cup sugar
2/3 cup balsamic vinegar
1 pound mascarpone cheese,* whisked to loosen
1 cup chilled heavy whipping cream
2 teaspoons vanilla extract
3 1-pint baskets fresh strawberries, hulled, thinly sliced
4 1/2-pint baskets fresh blueberries
Powdered sugar

Instructions

Preheat oven to 350 °F. Line 2 large baking sheets with parchment paper. Place 1 phyllo sheet on work surface (cover remaining phyllo with plastic wrap, then damp kitchen towel). Brush phyllo sheet with some melted butter and sprinkle with 1/2 teaspoon sugar. Top with second phyllo sheet. Brush with some melted butter and sprinkle with 1/2 teaspoon sugar. Repeat with 2 more phyllo sheets, brushing each with melted butter and sprinkling each with 1/2 teaspoon sugar. Cut phyllo stack in half lengthwise; cut crosswise into thirds, creating six 4 1/4-inch squares. Transfer squares to 1 prepared baking sheet, spacing evenly apart. Repeat with 4 more phyllo sheets to create 6 more squares; transfer to second baking sheet, spacing evenly apart. Bake phyllo until light golden, about 7 minutes. Using spatula, transfer phyllo stacks to rack and cool completely. Repeat with remaining phyllo sheets, butter, and sugar to make 36 squares total. (Phyllo squares can be made up to 2 days ahead. Store between layers of waxed paper in airtight container at room temperature.)
Bring vinegar and 4 teaspoons sugar to boil in small saucepan over medium-high heat. Reduce heat to low and simmer until syrupy and reduced to 1/4 cup, about 25 minutes. Refrigerate until cold, about 1 hour. (Can be prepared 1 day ahead. Refrigerate.)
Beat mascarpone, cream, vanilla extract, and remaining 1/2 cup sugar in large mixing bowl until stiff peaks form. (Mascarpone filling can be prepared 1 day ahead. Cover and refrigerate.)
Set aside 1/4 of strawberries and blueberries for garnish. Place 12 phyllo squares on work surface. Spread each with 1 tablespoon mascarpone filling. Cover with remaining sliced strawberries. Spread 1 tablespoon filling over strawberries. Place another 12 phyllo squares atop filling with corners slightly askew to bottom square. Spread each square with 1 tablespoon filling. Cover with remaining blueberries. Spread 1 more tablespoon filling over blueberries. Top with final 12 phyllo squares with corners slightly askew to middle square. (Can be made 3 hours ahead. Place napoleons on 2 large baking sheets. Cover and refrigerate.)
Spoon dollop of filling atop each napoleon. Garnish with reserved straw-berry slices and blueberries. Dust with powdered sugar. Place 1 napoleon in center of each plate. Drizzle balsamic reduction around edge of plates.
*Italian cream cheese, available at Italian markets and many supermarkets.