In a food processor, process butter, confectioners' sugar, and salt until smooth. Add flour and pulse until a dough forms. Stir in pistachios. Shape dough into two 8-inchlong logs, tightly wrap in plastic, and freeze until firm, 30 minutes (or up to 1 month).
Preheat oven to 350 degrees, with racks in upper and lower thirds. Cut dough into 1/4-inch slices and transfer to parchment-lined baking sheets. Bake until cookies are set and barely golden at edges, 10 to 15 minutes, rotating sheets halfway through. Let cool completely on sheets on wire racks.
Spread 1/2 teaspoon jam on bottoms of half the cookies, then sandwich with remaining cookies.
Store in airtight containers, up to 1 week.