In a mixer, add the softened butter and peanut butter and blend until smooth.
Next, add in sugar, brown sugar and cream until smooth. Scrap the sides to make sure everything is mixed.
After that, add in the vanilla, egg and milk. Mix on medium until incorporated.
Mix in baking soda, salt and SLOWLY add in flour, scraping the sides until the dough comes together.
Next, place cookies 2 inches apart on your cookie sheet and bake at 350°F for 10-15 minutes. *Edges will start to brown.
Let the cookies cool 10-15 minutes before enjoying.