Instructions

1. Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking pan thoroughly with butter or line with parchment paper, ensuring sides are covered for easy removal.
2. In a large microwave-safe bowl, melt the unsalted butter completely. Use 30-second intervals, stirring between each to prevent burning.
3. Add sugar to the melted butter and whisk vigorously until the mixture becomes smooth and slightly lighter in color, about 2-3 minutes.
4. Crack the eggs into the butter-sugar mixture one at a time, beating well after each addition. Stir in the peppermint extract, mixing until fully incorporated.
5. In a separate bowl, sift together the all-purpose flour, cocoa powder, and salt to remove any lumps and ensure even distribution.
6. Gradually fold the dry ingredients into the wet mixture, stirring gently until just combined. Avoid overmixing to maintain a tender texture.
7. Fold in both the chocolate chips and mint chocolate chips, reserving a small handful for topping.
8. Pour the batter into the prepared baking pan, spreading evenly with a spatula. Sprinkle the reserved chips on top for additional chocolate coverage.
9. Bake in the preheated oven for 25-30 minutes. Check for doneness by inserting a toothpick into the center - it should come out with a few moist crumbs.
10. Remove from oven and let cool completely in the pan for at least 1 hour. This allows the bars to set and makes cutting easier.
11. Once cooled, cut into 24 equal squares using a sharp knife. For clean cuts, wipe the knife between slices.
12. Store in an airtight container at room temperature for up to 5 days, or refrigerate for extended freshness.