Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and line a 9x9-inch (23x23 cm) square baking pan with parchment paper, leaving some overhang on the sides for easy removal.
Prepare the Brownie Batter:
In a medium-sized microwave-safe bowl, melt the butter in 30-second intervals until completely melted.
Stir in the granulated sugar until well combined.
Add the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, and salt.
Gradually add the dry ingredients to the wet ingredients, stirring until the batter is smooth and well combined.
Prepare the Candy Cane Swirl:
In a small microwave-safe bowl, combine the crushed candy canes and sweetened condensed milk.
Microwave in 20-second intervals, stirring each time, until the candy canes are completely melted and the mixture is smooth. This should take about 1-2 minutes.
Set aside to cool slightly.
Assemble the Brownies:
Pour about two-thirds of the brownie batter into the prepared baking pan, spreading it evenly.
Drizzle the candy cane swirl mixture over the brownie batter.
Drop spoonfuls of the remaining brownie batter on top of the candy cane swirl.
Use a knife or a toothpick to create swirls by gently dragging it through the brownie batter and candy cane mixture, creating a marbled effect.
Bake:
Place the baking pan in the preheated oven and bake for 30-35 minutes or until a toothpick inserted into the center comes out with a few moist crumbs attached. Be careful not to overbake; you want them to be fudgy.
Cool and Serve:
Allow the brownies to cool completely in the pan on a wire rack.
Once cooled, use the parchment paper overhang to lift the brownies out of the pan.
Cut into squares or rectangles, and serve.