Preheat oven to 350°. Cream butter and sugar until light and fluffy. Beat in eggs and extracts. In another bowl, whisk flour, baking powder and salt; gradually beat into creamed mixture.
Drop dough by tablespoonfuls 2 in. apart onto parchment paper-lined baking sheets; flatten slightly with bottom of a glass dipped in sugar. Bake until edges begin to brown slightly, 12-14 minutes. Remove from pans to wire racks; cool completely.
For filling, in a large bowl, beat mascarpone cheese and butter until smooth. In a small bowl, dissolve instant coffee in vanilla; beat into mascarpone mixture. Gradually beat in confectioners’ sugar until smooth. Pipe or spread filling on bottoms of half of the cookies; cover with remaining cookies. Dust cookies with cocoa. Store in the refrigerator.