Step 1: In a microwave-safe bowl, melt ½ cup unsalted butter and 2 cups semisweet chocolate chips in 15-second bursts, stirring well after each, until silky smooth. Set aside to cool.
Step 2: In a separate, medium-sized bowl, whisk together all-purpose flour, unsweetened cocoa powder, baking powder, and ¼ tsp salt until evenly distributed. Set aside.
Step 3: In a large bowl (or stand mixer), beat the light brown sugar, eggs, and 1 ½ tsp vanilla extract until nicely combined and a bit fluffy, about a couple of minutes.
Step 4: Mix in the cooled chocolate mixture until it's one beautiful, glossy chocolate dough.
Step 5: Gradually add the dry ingredients from Step 2 into the wet mixture on low speed until just combined. Do not overmix.
Step 6: Cover the chocolate cookie dough and refrigerate for at least 1 hour.
Step 7: When the dough is ready, preheat oven to 325°F (160°C). Line baking sheets with parchment paper.
Step 8: Use a medium cookie scoop (size 50) to portion the dough, roll into balls, and place them about 2 inches apart on the prepared baking sheets.
Step 9: Bake for 13-16 minutes, or until the tops look set. Let them cool on the baking sheet for about 10 minutes before transferring to a wire rack to cool completely.
Step 10: While cookies cool, in a bowl, beat the creamy peanut butter and 6 tablespoons room temperature unsalted butter until smooth and creamy.
Step 11: Mix in 1 tsp vanilla extract and a pinch of salt.
Step 12: Gradually add the confectioners' sugar, mixing on low speed until the mixture is well combined and forms a soft, rollable dough.
Step 13: Roll the peanut butter mixture into 1-inch balls, then gently flatten each into a thick disk. Gently press these peanut butter disks onto the tops of your completely cooled chocolate cookies.
Step 14: For the ganache, place 1 ½ cups semisweet chocolate chips in a heatproof bowl.
Step 15: In a small saucepan, heat ½ cup heavy whipping cream over medium-low heat until it starts to steam, just before boiling. Remove from heat.
Step 16: Pour the hot cream directly over the chocolate chips. Let it sit for 5 minutes without stirring.
Step 17: After 5 minutes, whisk gently until the mixture is beautifully smooth and glossy.
Step 18: Spoon a generous amount of ganache over each cookie, letting it drip down the sides for a classic Buckeye look.
Step 19: Let the ganache set for 30-60 minutes at room temperature before serving.