1. Prepare the Puff Pastry

• Thaw puff pastry on the counter until soft but still cold.
• Place one sheet on top of the other and roll them gently with a rolling pin until they reach 12×16 inches. Doubling the sheets creates taller pastry shells.
• Using a 3-inch cookie cutter, cut out circles as closely as possible to minimize scraps.
• Transfer circles onto a parchment-lined baking sheet, leaving 1-inch space between each.

2. Create the Pastry Borders

• Using a 2-inch cookie cutter, press gently into the center of each circle without cutting all the way through. This indentation helps form a well for the filling.

3. Apply the Egg Wash and Sugar

• Beat the egg and brush it over the tops of the circles using a pastry brush (or a scrunched-up paper towel).
• Sprinkle granulated sugar on top for a golden, slightly caramelized crust.

4. Bake the Puff Pastry

• Preheat the oven to 425°F (220°C).
• Bake for 15 minutes, or until the pastries puff up and turn golden brown.
• Once out of the oven, use your fingers or the smaller cookie cutter to gently press down the center, leaving the raised edges intact.
• Let pastries cool completely before assembling.

5. Prepare the Chocolate Ganache

• In a small saucepan, heat 1/2 cup heavy cream until it’s almost boiling.
• Pour over 1/2 cup chocolate chips and let sit for 2-3 minutes before stirring until smooth.
• Transfer the ganache into a zip-lock bag, snipping off a small corner to create a piping bag.

6. Make the Chantilly Cream

• In a mixing bowl, combine 2 cups heavy cream, 2/3 cup sugar, and 1 tablespoon vanilla extract.
• Whip on high speed until stiff peaks form.
• Transfer to a piping bag with a star tip (or a zip-lock bag with a corner snipped off).

7. Assemble the Tarts

• Pipe a generous drizzle of ganache into each pastry shell, reserving some for decoration.
• Fill each tart with Chantilly cream, piping it in a circular motion for a professional look.
• Top each tart with one raspberry and two blueberries.
• Drizzle the remaining ganache over the berries in thin lines for added elegance.

8. Add the Finishing Touches

• Lightly dust the tarts with powdered sugar before serving.
• Garnish with fresh mint leaves if desired.
• Refrigerate until ready to serve.