Preheat your oven to 350°F (175°C). In a medium bowl, combine the graham cracker crumbs, melted butter, and granulated sugar. Mix until well combined.

Press the mixture firmly into the bottom and up the sides of a 9-inch tart pan. Bake for 10 minutes, then remove from the oven and let cool completely.

In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer. Remove from heat and add the chopped chocolate. Let it sit for 2-3 minutes, then stir until smooth and fully combined.

Pour the chocolate ganache into the cooled crust, spreading it evenly. Refrigerate for at least 2 hours, or until the ganache is set.

Once set, top the tart with fresh blueberries and dust with powdered sugar. Garnish with mint leaves if desired.

Slice and serve chilled or at room temperature.