Place melted butter in a medium bowl. Add both sugars and mix on low speed till smooth. Mix in eggs and vanilla extract till combine. Mix flour, baking soda and salt salt together and slowly mix in flour, 1/2 cup at a time. Mix in chocolate chips.

Using a medium ice-cream scooper, scoop 20 balls into a large Pyrex and chill for 20 min.

While cookies chill make the frosting. Beat butter till fluffy. Add in brown sugar, vanilla extract, milk, and salt. Continue to beat for about 8 min. Microwave flour in a small bowl for 90 secs. This heat treats the flour. Pour flour into mixture, with powder sugar and beat for another 3 min till smooth. Place in piping bag and put in the fridge.

Take the cookies out of the fridge or freezer and place on two large baking sheets with parchment paper. Bake for 18 min. Check at 15 min and max baking for 20 min. Half way thru baking I press down the cookie with a back of a measuring cup to flatten them. Then let them cool for 15-20 minutes. Pipe cookie dough frosting on a bottom of a cookie and place another cookie on top.