In a large bowl, cream butter and sugar until light and fluffy. Beat in the egg, milk and extract. Combine the flour, baking powder and salt; gradually add to creamed mixture and mix well. Cover and refrigerate for 4 hours or until easy to handle.
Divide the dough in half. On a lightly floured surface, roll out each portion to 1/4-in. thickness. Cut with 2-1/2-in. acorn cookie cutter. Place 1 in. apart on ungreased baking sheets.
Bake at 375° for 8-10 minutes or until edges are firm. Remove to wire racks to cool completely.
In a microwave, melt chocolate chips; stir until smooth. Spread chocolate over the stem and cap of each acorn, leaving about a 1/4-in. border. Sprinkle pecans over chocolate. Pipe remaining chocolate in a criss-cross pattern over each acorn. Let stand until firm.