Lightly grease a 9-by-13-inch baking pan with butter or nonstick cooking spray. Line it with parchment paper, leaving a little overhang on the sides.

The parchment makes it easier to lift the finished treats out of the pan and cut them into neat squares.

Set the pan aside while you prepare the chocolate mixture.

Step 2: Melt the Butter and Marshmallows

Place the butter in a large saucepan over low heat.

Once the butter has melted, add the mini marshmallows. Stir continuously with a heat-resistant spatula until the marshmallows are almost completely melted and the mixture looks smooth.

Keep the heat low. High heat can make marshmallows tough and produce hard Rice Krispie treats after they cool.

Step 3: Add the Chocolate

Remove the saucepan from the heat.

Add the semisweet chocolate chips and stir until they melt into the warm marshmallow mixture. Add the cocoa powder, vanilla extract, and salt.

Continue stirring until the mixture is smooth, glossy, and evenly chocolate-colored.

If the chocolate chips do not melt completely, allow the mixture to sit for a few seconds before stirring again. Avoid placing the saucepan back over high heat.

Step 4: Fold in the Rice Krispies

Pour the Rice Krispies cereal into the saucepan.

Using a large spatula, gently fold the cereal into the chocolate marshmallow mixture until every piece is coated.

Work carefully but quickly so the cereal stays crispy and the mixture doesn’t become too firm before you transfer it to the pan.

Step 5: Add the Christmas Candies

Fold in approximately half of the red and green candy-coated chocolates.

Reserve the remaining candies for decorating the top. Adding some candies to the mixture gives every square a little extra color and crunch.

If the chocolate mixture is still very warm, allow it to cool slightly before adding the candies to reduce the chance of their coatings becoming damaged.

Step 6: Press the Mixture into the Pan

Transfer the chocolate cereal mixture to the prepared baking pan.

Lightly grease your hands or the back of a spatula with butter or nonstick cooking spray. Gently press the mixture into an even layer.

Do not pack it down too firmly. Pressing too hard can make the finished treats dense and difficult to bite.

Step 7: Add the Christmas Decorations

Scatter the reserved red and green candies and Christmas sprinkles evenly over the top.

If you’re using white chocolate, melt it in a microwave-safe bowl in 15- to 20-second intervals, stirring after each interval until smooth.

Drizzle the melted white chocolate over the cereal mixture in decorative lines.

Add a few extra sprinkles while the drizzle is still wet so they stick properly.

Step 8: Let the Treats Set

Allow the mixture to cool at room temperature for approximately 30 to 45 minutes, or until firm enough to cut.

You can refrigerate the pan for about 15 to 20 minutes if you want to speed up the process, but avoid leaving it in the refrigerator too long because the treats may become harder.

Step 9: Cut and Serve

Use the parchment paper overhang to lift the entire slab out of the pan.

Place it on a cutting board and use a sharp knife to cut it into 16 squares or smaller bite-sized pieces.

For a Christmas party, you can also use lightly greased cookie cutters to create festive shapes once the mixture has set enough to hold its shape.

Arrange the finished treats on a serving platter and enjoy!