Preheat oven to 375°F. Prepare a baking sheet with parchment paper and set aside. Do not spray with nonstick spray, this will cause the cookies to spread when baking.
Combine the flour and salt in a small bowl. Mix the butter until smooth in a bowl of a stand mixer. Add the sugar and mix until well combined.
Add the vanilla extract and egg. Add the flour and mix until just combined.
Take about 1 to 2 tablespoons worth of dough and roll it up in a ball. Toss in the coarse sugar and make sure all sides are covered.
Place on the prepared baking sheet and lightly press down in the center with your thumb. This will give the indentation needed for the chocolate while flattening the cookie. You want the indent to be about a ¼ inch deep. Repeat until all the dough is used.
Place in the oven and bake for 12 to 15 minutes, or until the cookies are slightly golden brown. After the cookies cook, the indent might have lost its form slightly. Use a spoon to re-push the holes. Make sure to do this while the cookies are warm because they will crack when cooled.
While the cookies are cooling, take a moment to make the ganache. Place the dark chocolate, heavy cream, salt, and butter in a saucepan. Melt until everything combines together. Remove from the heat and mix in the vanilla extract.
Use a spoon to add the chocolate ganache to each of the cookie indents. Allow them to set for about one hour.
