You can store these fudgy brownies for up to three days. Place them in a tightly covered container to keep them from drying out.
Preheat oven according to cookie package directions. On a lightly floured surface, use hands to slightly flatten cookie dough to an 8x2-1/2-inch log. Place on baking sheet, then freeze for 30 minutes. Slice dough in half lengthwise, then slice each half in 16 slices. Place slices on cookie sheets. Using a fork dipped in granulated sugar, make a crisscross pattern on each cookie. Bake cookies according to package directions or until golden brown. Cool on wire racks.
Meanwhile, in a medium saucepan stir butter and chocolate over low heat just until melted. Remove from heat. Using a wooden spoon, stir in sugar and vanilla. Cool 5 minutes.
Set oven to 350°F. Line the bottom and sides of an 8x8x2-inch baking pan with heavy foil, extending foil over pan edges. Grease foil; set pan aside.
Add eggs, one at a time, to butter-chocolate mixture, beating after each just until combined. Stir in flour and cocoa powder. Evenly spread batter in prepared pan.
Bake for 30 to 35 minutes, just until a wooden toothpick inserted near center comes out clean. Transfer to wire rack. Leave oven set to 350°F to warm sandwich cookies.
For sandwich cookies, scoop and mash warm brownie onto the flat side of a cookie. Top with 1 tsp. jam and a second cookie. Place sandwich cookies that will be served immediately on a cookie sheet and warm in oven about 4 minutes.
Store leftover brownies in a covered container up to 3 days.
Place any assembled cookies you are not warming through in an airtight container. Refrigerate up to 2 days. Place on a baking sheet and heat in a 350°F oven about 5 minutes or until warmed through.