Heat oven to 375ºF. Line two baking sheets with parchment.
In a large mixing bowl, beat together butter, peanut butter and sugars on medium speed until light, about 2 minutes.
Add egg and vanilla 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.
Alternatively melt chocolate chips and use a bamboo skewer dipped in melted chocolate to draw eyes on the cooled cookies.
Alternatively to mini chocolate chips: melt chocolate chips and use a bamboo skewer dipped in melted chocolate to draw eyes on the cooled cookies.Reindeer cookies can be made ahead. Store in an airtight container at room temperature, in single layers separated by waxed paper, up to 2 days.