Preheat the oven to 350°F. Line baking sheets with parchment or silicone baking mats.
In a medium bowl combine the flour, baking soda, and salt.
In the bowl of an electric mixer, beat the butter, peanut butter, brown sugar, and granulated sugar on medium-high speed until very well combined, about 2 minutes. Add the eggs, milk, and vanilla and beat until combined. On low speed gradually add the flour mixture and beat until just combined. Add the chocolate chips, peanut butter chips, and Reese’s Pieces and beat until combined. You may need to do this by hand with a spatula if your mixer isn’t strong enough.
Roll the dough into 1/4-cup balls and place on the prepared baking sheets. Flatten the dough balls into 1/2-inch thick disks. (At this point the dough can be frozen.) Bake for 12 to 15 minutes, or until the cookies are light golden brown at the edges. Place the baking sheets on cooling racks and let cool completely. Store the cookies in an airtight container at room temperature for up to 5 days.