In a bowl of a stand mixer, put butter and powdered sugar.
Whisk until creamy then add the egg, salt, and vanilla extract.
Whisk more for few minutes.
Add flour and baking powder then mix everything together until well incorporated.
Place the very soft sticky batter in a piping bag fitted with a large pastry star tip (about 1/2 inch).
Pipe in a non stick baking pan.
Pipe in the same spot by pressing down to obtain rosette shaped cookies.
To shape the dough into shells, pipe a small amount of batter in one spot, then slide the piping bag down. Fix the end of the shell with your 2 fingers.
Bake at 350°F preheated oven for 15 to 25 minutes or until golden.
Let cool.
Put a small amount of jam or fruit preserves on the base of one cookie then sandwich it with the other cookie.
Dip the shell shaped cookies halfway or less into the melted chocolate.
Let set.
Enjoy.