Preheat the oven to 350℉. Line 3 baking sheets with parchment paper templates, and set aside.
Whisk together the flour and salt, and set aside.
Cream the butter and powdered sugar until light and creamy, about 3 minutes on medium speed. Add the eggs and mix for another 3 minutes on low speed. Add the vanilla and the melted butter, and mix for 1 minute on low. Add the flour and salt and mix just until the flour is mixed in.
Fit a piping bag with a large ½" round piping tip and fill it with the cookie batter.
Pipe 2-inch-long cookies, two inches apart on the parchment paper. Bake for 10 minutes. Turn off the oven and open the door slightly. Leave the cookies in the oven to dry out for about 20 minutes. Check the cookies periodically so they don't get too brown.
Add the chocolate and heavy cream to a medium microwave-safe bowl. Microwave for 30 seconds then whisk together. If needed, microwave for another 30 seconds until the chocolate is completely melted. Stir until the ganache is glossy. Set aside to thicken but not completely.
Once the cookies are cool, pair them and lay them out so they can be filled. Pour the ganache into a piping bag, cut a tiny hole, and carefully cover the bottom inside of the cookies, leaving a small edge. Place the other cookie on top and gently press together.