Chocolate-Pecan Ice Cream Sandwiches

Preheat oven to 350 degrees F. Grease large cookie sheet. Place 2 jelly-roll pans or cookie sheets in freezer to use later for ice cream. In microwave-safe large bowl, combine butter, chocolate chips, and sweetened condensed milk. Cook in microwave oven on High 1 minute; stir. Microwave 30 to 60 seconds longer and stir again until chocolate and butter are completely melted. Into chocolate mixture in bowl, stir pecans, flour, and vanilla until combined. Drop dough by rounded measuring tablespoons, 2 inches apart, onto greased cookie sheet. With fingers, press each mound into 2-inch round. Bake cookies 10 to 12 minutes or until firm when lightly pressed. Cool on cookie sheet on wire rack 2 minutes. With metal spatula, transfer cookies to wire rack to cool completely. Repeat with remaining dough. Store cookies between layers of waxed paper in tightly covered container at room temperature until ready to use or up to 2 weeks, or freeze up to 3 months. Meanwhile, scoop ice cream by rounded 2 tablespoons into 24 mounds onto cold jelly-roll pans; flatten each mound into 2-inch round. Freeze ice cream rounds until firm, at least 1 hour. If not using right away, store ice cream rounds in freezer-safe container with waxed paper between layers, up to 1 week. Just before serving, assemble ice cream rounds and cookies into 24 sandwiches.