Preheat oven to 375°F. In a bowl, combine flour, baking soda, and salt. In a stand mixer, combine brown sugar, peanut butter, butter, milk, and vanilla. Mix until blended.
Next, add the egg and beat until just blended.
Next, add the flour mixture into the wet ingredients.
Mix the dough until well combined but do not overmix.
Form dough into 2-inch balls. Shape into a rounded triangle and flatten slightly with your hand. Space cookies about 2-inches apart on a greased cookie sheet and bake for 8 to 10 minutes.
Remove cookies from oven and immediately gently press two mini pretzels into the tops of the cookies for the reindeer’s antlers.
Finally, press two chocolate chips in for the eyes and one red M&M for the nose.
Allow the cookies to cool before eating.