Preheat oven to 350°F (175°C). In a medium bowl, combine chocolate cookie crumbs, melted butter, and sugar until the mixture resembles wet sand and holds together when pressed.

Press the crumb mixture firmly and evenly into the bottom and up the sides of a 9-inch tart pan with removable bottom. Use the bottom of a measuring cup to compact it smoothly.

Bake the crust for 10-12 minutes until it looks set and smells fragrant. Remove from oven and let cool completely on a wire rack, about 30 minutes.

Place the chopped dark chocolate in a large heatproof bowl. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer with small bubbles forming around the edges, about 3-4 minutes.

Pour the hot cream over the chopped chocolate and let it sit undisturbed for 2 minutes to soften the chocolate. Add the salt, then stir gently in one direction with a spatula until completely smooth and glossy.

Pour the ganache into the cooled tart shell, tilting the pan gently to spread it evenly to the edges. Tap the pan lightly on the counter 3-4 times to release any air bubbles.

Refrigerate the tart uncovered for at least 3 hours or overnight until the ganache is firm and set. Once set, you can cover it loosely with plastic wrap.

Before serving, let the tart sit at room temperature for 10-15 minutes. Remove the outer ring of the tart pan and transfer to a serving plate. Slice with a hot, dry knife, wiping it clean between cuts for neat slices.