Preheat oven to 350°F. Line two baking sheets with parchment paper.
Make the Cookie Dough
Melt 1 cup butter and let cool slightly.
In a mixer, beat melted butter, brown sugar, and granulated sugar until smooth.
Add eggs one at a time, then vanilla; mix well.
Add flour, cocoa powder, baking soda, and salt. Mix on low until just combined.
Fold in 2 cups chocolate chips.
Bake the Cookies
Using a ¼-cup cookie scoop (about 65 g of dough), scoop 20 mounds onto the sheets, spacing them 2–3 inches apart.
Press gently to about ½ inch with your hand
Bake 11–12 minutes, until centers are set but still soft.
Let cookies cool completely on the sheet.
Prepare the Peanut Butter Filling
In a clean bowl, beat ½ cup butter and peanut butter until smooth.
Add powdered sugar and vanilla. Mix on low, then medium, until thick like frosting.
Make the Ganache
In a microwave-safe bowl, combine chocolate chips and cream.
Microwave 1 minute, stir; heat another 15–30 seconds if needed.
Stir until glossy and smooth. Let cool to room temperature.
Assemble the Cookies
Spread a thin layer of peanut butter filling on each cookie.
Top with a spoonful of ganache and smooth it out.
Let sit at room temperature until the ganache sets.
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Recipe Notes
Storage: Store your Buckeye brownie cookies in an airtight container at room temperature for up to 3 days, or refrigerate for up to 7 days. Layer with parchment paper to keep the peanut butter filling and ganache from sticking.