Step 1: Preheat your oven to 350°F (175°C).
Step 2: In a large mixing bowl, cream together the unsalted butter, light brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes.
Step 3: Add the creamy peanut butter, vanilla extract, and milk, and beat until well combined.
Step 4: Incorporate the egg and mix until fully combined.
Step 5: In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add to the wet mixture and mix on low until just combined.
Step 6: Scoop the dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart. Press down with a fork to create a crisscross pattern.
Step 7: Bake for 10-12 minutes until the edges are lightly golden.
Step 8: Allow to cool on the baking sheet for 5 minutes before transferring to a wire rack.