1. Preheat the oven to 325°F. Line a baking sheet with parchment paper.
In a small bowl, whisk together sugar and cornstarch; set aside. Using an electric mixer, whip egg whites on medium-high speed until soft peaks form, about 3 minutes. Continue to whip, gradually adding sugar mixture 1 tablespoon at a time, until stiff peaks form. Beat in lemon juice.
2. Spoon mixture into a large piping bag or a large resealable plastic bag. Cut open tip of piping bag about 1/2 inch wide. Pipe ghost mounds about 2 inches high onto the prepared baking sheet. Use dried blueberries and/or currants to make eyes and mouths.
3. Place in the oven and lower heat to 225°F. Bake for 1 hour. Turn the oven off and prop the door open, using a wooden spoon to keep the door open if needed. Let meringues cool completely in the oven. Meringue ghosts will keep in an airtight container at room temperature for up to 3 days.