Pressure cooker method: Remove the top of the can of sweetened condensed milk. Cover with aluminum foil.
Add the cooking rack to the bottom of a pressure cooker or Instant Pot. Add the prepared can. Pour water in the pressure cooker until about halfway up the side of the can. (for stovetop method, see note*)
Cover tightly, making sure the steam vent is closed.
Cook on high for 60 minutes. Allow the steam to vent naturally. Once the can has cooled, remove from the pressure cooker.
Stir in the vanilla and salt, refrigerate until ready to use.
Preheat the oven to 375° F.
Separate the eggs. Add the salt to the whites and beat the whites until light and frothy.
While beating the whites add ½ cup powdered sugar to the whites a little at a time, beat until firm.**
Add the remaining powdered sugar and cocoa powder, stir until combined.
Stir in the vanilla, beer, and egg yolks until well combined.
Line a baking sheet with parchment paper. Use a cookie scoop to mound cookies onto the parchment.
Bake for 14 minutes. Pull the parchment onto the counter to allow the cookies to cool.
Spread the filling between two cookies. Refrigerate until ready to serve.