01Adjust the oven rack to the 2nd level position and pre-heat the oven to 350ºF.
02 Line cookie sheets with parchment paper. Set aside.
03In a medium bowl, whisk together the flour, baking soda, baking powder, cinnamon, and salt. Set aside.
04Using your hand-held mixer or a stand mixer fitted with the paddle attachment, cream the butter, sour cream, and peanut butter on medium- to medium-high speed until smooth and well-blended.
05Add in the brown sugar, granulated sugar, egg, milk, and vanilla extract, and mix until fully incorporated.
06Set the mixer speed to low and add in the dry mixture a little at a time until completely blended. The peanut butter sour cream cookie dough should be light and fluffy in texture.
07Roll the cookie dough into 1" balls and space them 1 ½”-2” apart on the cookie sheet. Pressing down gently, make a criss-cross or “X” pattern with a fork, that’s been dipped in cold water, over top of the cookie dough ball.
08Bake the peanut butter sour cream cookies for 10-12 minutes at 350ºF. Cookies should be a nice golden brown in color. Let cool on the cookie sheets for about 5 minutes before transferring them to a cooling rack to cool completely.