Heat oven to 375ºF. Grease two baking sheets. In a large mixer bowl beat together butter, peanut butter and sugars on medium speed until light, about 2 min. Add egg and extract; beat until combined. Stir in flour, baking soda and salt until a dough forms. Roll into 1-inch balls and place 1 inch apart on prepared sheets.
Bake, one sheet at a time, until just set and bottoms are golden, 8 to 10 min. For each cookie, immediately place 1 M&M in center for nose, 2 chocolate chips for eyes and 2 pretzel pieces on top for antlers. Transfer cookies on sheets to a wire rack and let cool completely. (Can be made ahead. Sore in an airtight container at room temperature, in single layers separated by waxed paper, up to 2 days.)