Step 1: First things first, preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Parchment is key here; it makes cleanup a breeze and helps the cookies bake evenly without sticking.
Step 2: In a large bowl, toss in your softened butter, creamy peanut butter, granulated sugar, and packed brown sugar. Now, beat them together with an electric mixer (handheld or stand mixer works!) until the mixture is light and fluffy. This usually takes 2-3 minutes. Scrape down the sides of the bowl as needed to make sure everything is combined.
Step 3: Crack in that large egg and pour in the vanilla extract. Beat them until they are just combined into the creamy mixture.
Step 4: In a separate, medium-sized bowl, whisk together your all-purpose flour, baking soda, and salt. Give it a good whisk to distribute the leavening evenly.
Step 5: Gradually add the dry ingredients to the wet ingredients. Mix on low speed (or mix by hand!) just until everything is combined. Stop mixing as soon as you see no more dry streaks of flour. Overmixing can lead to tougher cookies, and we want these soft!
Step 6: Now for the fun part! Gently fold in the Reese's pieces. I like to use a spatula for this step, just making sure they are evenly distributed throughout the dough without crushing them too much.
Step 7: Scoop the dough into large balls. I aim for about 3 tablespoons per cookie, which makes a nice substantial cookie. Place them on your prepared baking sheet, leaving a few inches between each as they will spread slightly. Gently press down on the top of each dough ball just a little bit to flatten it slightly.
Step 8: Pop the baking sheet into your preheated oven. Bake for 10-12 minutes. You'll know they're done when the edges are lightly golden, but the centers still look quite soft and maybe even a little underdone. This is crucial for that super soft, chewy middle!
Step 9: This is important! Leave the cookies on the hot baking sheet for about 10 minutes after they come out of the oven. They continue to cook and set up during this time. Then, carefully transfer them to a wire rack using a spatula to cool completely. Resisting the urge to eat one now is the hardest part!
Step 10: While the cookies cool, make the drizzle. Put the remaining creamy peanut butter in a small microwave-safe bowl. Heat it in the microwave in 15-second bursts, stirring well after each, until it's melted and smooth. If it's still a bit thick for drizzling, stir in 1-2 teaspoons of coconut oil or neutral oil until it reaches a nice, pourable consistency.
Step 11: Once the cookies are completely cooled, grab a spoon or fork and drizzle that lovely melted peanut butter all over the tops. Let the drizzle set for a little while (maybe 15-20 minutes) before stacking or serving. This prevents a sticky mess!