In a large bowl, combine the 3/4 cup butter and the 3/4 cup powdered sugar. Beat with an electric mixer on medium speed until well mixed, scraping side of bowl occasionally.

Add egg; beat until combined. Gradually beat in flour and salt on low speed until well mixed. Cover and chill about 1 hour or until dough is easy to handle.

Preheat oven to 350 degrees F. Place pistachio nuts in a small bowl. Shape dough into 1/2-inch balls. Roll each ball in pistachio nuts to coat. Place balls 1 inch apart on an ungreased cookie sheet. Dip the bottom of a glass in granulated sugar and flatten each cookie.

Bake in preheated oven for 8 to 9 minutes or just until edges begin to turn golden brown. Transfer to a wire rack; let cool.

While cookies are cooling, prepare filling: In a small bowl, combine the 1-1/4 cups powdered sugar, the 1/4 cup butter, and the vanilla. Beat in enough of the maraschino cherry juice to make a filling of desired consistency. Reserve about 1/4 of the filling for decorating cookies.

Spread about 1 teaspoon of the remaining filling on the bottom of each of half of the cookies. Top with remaining cookies, flat sides down, pressing lightly together. Before serving, spoon a small amount of the reserved filling on top of each assembled sandwich cookie. If desired, press a maraschino cherry into filling. Makes about 21 sandwich cookies.

To Store: Layer cookies between waxed paper in an airtight container; cover. Store in the refrigerator for up to 3 days or freeze for up to 3 months.