1. Preheat the oven to 350°F and line a 9×9-inch baking pan with parchment paper.

2. Melt the butter and dark chocolate together until smooth, then let the mixture cool slightly.

3. Whisk in the granulated sugar until glossy.

4. Add the eggs one at a time, whisking well after each one. Stir in the vanilla extract.

5. Fold in the plain flour, cocoa powder, and salt just until combined.

6. In a separate bowl, melt the Mint Aero chocolate and stir in the sweetened condensed milk, peppermint extract, and optional green food coloring until smooth.

7. Spread about two thirds of the brownie batter into the prepared pan.

8. Spoon the mint mixture over the brownie layer and spread gently into an even layer.

9. Dollop the remaining brownie batter on top and spread carefully to cover most of the mint layer.

10. Sprinkle the chocolate chips over the top.

11. Bake for 30 to 36 minutes, until the edges are set and the center still looks slightly soft.

12. Cool completely in the pan, then chill for cleaner slices if desired.

13. Lift out, slice, and serve.