• Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
• In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl using a hand mixer), beat butter, granulated sugar, and light brown sugar until light and fluffy.
• Add eggs and vanilla extract, mixing until fully combined.
• In a separate medium bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.
• Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
• Using a 1-tablespoon cookie scoop, drop the dough onto the prepared baking sheets, spacing cookies about 2 inches apart.
• Bake for 8 to 10 minutes, until the edges are set but the centers still look slightly soft.
• Remove from the oven. Let the cookies cool completely on the baking sheets, about 20 to 30 minutes.

Mint Filling

• In a medium bowl, using a hand mixer, beat butter until smooth.
• Add confectioners’ sugar, peppermint extract, and kosher salt. Mix until creamy and fluffy.
• Add green gel food coloring one drop at a time, mixing until you reach your desired minty green shade.
• Using a 1-tablespoon scoop, place a ball of mint filling in the center of each cooled cookie. Gently press and spread the filling slightly, leaving a small border around the edges.

Chocolate Ganache

• Fill a pot about halfway with water and bring to a simmer over low heat. Place a heat-safe bowl (glass or stainless steel) over the pot, making sure the bottom of the bowl does not touch the water.
• Add chocolate chips and butter to the bowl. Stir continuously with a rubber spatula until melted and smooth, about 5 minutes.
• Remove the bowl from heat once the ganache is smooth.
• Spoon a small amount of ganache over each mint filling center, just enough to cover it.
• Let the cookies sit at room temperature until the ganache is set, or refrigerate briefly if you want to speed up the setting process.