Fudgy Chocolate Peanut Butter Sandwich Cookies Recipe

For the Cookies:

2¼ cups all purpose flour
½ tsp table salt
1 tsp baking soda
1 cup (2 sticks) salted butter, slightly softened
½ cup granulated sugar
1 cup packed brown sugar
2 large eggs, beaten, room temp
1 TB pure vanilla extract
½ cup unsweetened real cocoa powder
1 cup milk chocolate chips

For the Filling:

1 cup salted butter, room temp
1 cup creamy peanut butter, room temp
3¾ cups powdered sugar
2-3 TB whole milk