Chocolate Fudge Pop Tart Bars

1. To make the filling. Combine the chocolate and cocoa powder in a bowl. Heat the milk in a pot set over medium heat until steaming, about 5 minutes. Pour the hot milk over the chocolate and whisk until the chocolate is melted. Whisk in the butter and vanilla. Set aside. 
2. To make the cookie dough. In a bowl using an electric mixer, beat together the butter and sugar until light and fluffy. Add the egg and vanilla, beat until incorporated. Add the flour, cocoa powder, and salt, beating until just combined. 
3. Preheat the oven to 350° F. Line a 9×9 inch baking dish with parchment paper. 
4. Divide the dough in half. Press half the dough into the prepared baking dish. Trace the 9x9 inch baking dish out on a sheet of parchment paper. Now roll the remaining dough out just past the edges of the traced-out square. Set aside.
5. Evenly spread the chocolate fudge over the dough in the baking dish. Carefully invert the reserved dough square over the filling, pressing down gently to secure. Trim away any excess dough. See photos above. 
6. Freeze the bars for 15 minutes. Bake foer 40 - 45 minutes, until just set in the center. Let cool. 
7. To make the frosting. In a bowl, whisk together the powdered sugar, cocoa powder, vanilla, and 3 tablespoons of water until smooth. Stir in the melted chocolate. If your frosting is too thick, thin with 1-2 tablespoons of additional water.
8. Spread the frosting over the pop-tart. Let set a few minutes, then top with salt/sugar. Let dry, then cut into bars. Serve or store in an airtight container for up to 3 days at room temperature.