1. Prepare Your Pan: Preheat your oven to 375°F (190°C). Line a 9x9-inch baking pan with parchment paper, allowing some overhang on the sides for easy lifting later.
2. Mix the Simple Dough: In a large mixing bowl, combine the sugar cookie mix, softened butter, and egg. Stir until everything is just blended together. Gently fold in the 1/2 cup of crushed candy canes until they're nicely distributed.
3. Bake to Perfection: Press this easy dough evenly into your prepared pan. Bake for 22-27 minutes, or until the edges are a light golden brown and the center looks firm. Let the cookie bars cool completely in the pan on a wire rack – this step is crucial for perfect frosting!
4. Whip Up the Creamy Frosting: While the bars cool, beat the softened butter in a medium bowl until it's light and fluffy. Gradually add the powdered sugar, starting with 1 tablespoon of milk or cream, the peppermint extract, and a pinch of salt. Beat until you have a smooth, spreadable frosting. If it's too thick, add a tiny bit more milk, a teaspoon at a time, until it reaches your desired consistency.
5. Frost and Garnish: Once your cookie bars are entirely cool, spread the dreamy peppermint frosting evenly over the top. Sprinkle generously with the remaining 2-3 tablespoons of crushed candy canes for a beautiful and festive finish.
6. Slice and Enjoy: Use the parchment paper overhang to gently lift the entire baked and frosted slab out of the pan. Slice into neat squares or rectangles. Serve these delightful bars and savor the simple, homemade goodness!