• Preheat oven to 225°F and line a baking sheet with parchment paper.

Make the meringue.

• In a small bowl, whisk together sugar and cornstarch. Set aside.
  1 cup granulated sugar, 1 Tablespoon cornstarch
• In the bowl of a stand mixer with the whisk attachment, beat egg whites on medium-high speed until foamy, about one minute.
  4 large egg whites
• Add cream of tartar and salt and beat until blended.
  ¼ teaspoon cream of tartar, ⅛ teaspoon salt
• Reduce speed to medium and gradually add the sugar mixture one Tablespoon at a time. Beat until stiff peaks form and the mixture becomes glossy, about one to two minutes.
• Add vanilla and beat until blended.
  ¼ teaspoon vanilla extract
• Scoop one quarter of the blackberry preserves and drop small amounts over the top of the meringue. Drag a spoon in a zig-zag pattern through the meringue so that the blackberry preserves are swirled into the top layer of meringue.
  ¼ cup blackberry preserves
• Scoop two portions of meringue (about 3 Tablespoons each) off the top and place onto the baking sheet. Made an indentation in the middle of each with the back of a spoon. Repeat the process of swirling the blackberry preserves into the meringue and scooping the meringue onto the baking sheet until you have eight meringues.
• Bake the meringues until the outsides are slightly golden and have formed a crust, about 1 hour and 30 minutes. Turn the oven off and let the meringues stand in the oven for 12 hours.

Make the whipped cream.

• Just before you're ready to assemble the meringues, make the whipped cream. In a large bowl, beat the cream and confectioner's sugar with an electric mixer on high speed until stiff peaks form. Set aside.
  1 cup heavy whipping cream, 1 Tablespoon confectioners' sugar

Assemble the meringues.

• Remove the baking sheet from the cooled oven and gently remove the meringues from the parchment paper using a spatula. Scoop a spoonful of whipped cream into the center of each meringue, then scoop a bit of lemon curd (about half a Tablespoon) on top. Garnish with blackberries and mint leaves. Serve immediately.
  ¼ cup lemon curd, 8 fresh blackberries, 8 mint sprigs