Tips for Best Results
- Use room-temperature butter so it creams smoothly with the sugars.
- Don’t overmix after adding flour; this keeps the bars tender instead of tough.
- Underbake slightly for gooey centers—the bars will continue to set as they cool.
- Press extra M&M’s on top before baking so the colors show clearly for a festive look.
Variations and Serving Ideas
- Swap some chocolate chips for white chocolate chips to brighten the look.
- Add chopped pretzels or peanuts for a salty-sweet twist.
- Drizzle cooled bars with melted white chocolate and sprinkle with crushed candy canes.
- Serve slightly warm with vanilla ice cream and extra M&M’s for a dessert-style plate.
Storage, Freezing, and Make-Ahead
- Store bars in an airtight container at room temperature for up to 4 days.
- Freeze sliced bars in a single layer, then transfer to a freezer bag for up to 2 months; thaw at room temperature.
- Great for make-ahead: bake the bars a day before an event, cool, cover, and slice just before serving for the freshest look.
Frequently Asked Questions
1. Can I use a different pan size?
A 9×13 pan gives standard bar thickness. A smaller pan (like 9×9) will produce thicker bars and need a longer bake time, while a larger pan will make thinner bars; adjust time accordingly.
2. Can I use salted butter instead of unsalted?
Yes. Reduce the added salt slightly (to about 1/2 teaspoon) to compensate for the salt in the butter.
3. How do I keep the bars from overbaking?
Start checking a few minutes early. Look for lightly golden edges and a center that looks set but still soft; the top shouldn’t be dark or dry. The bars firm up as they cool.
4. Can I make these without chocolate chips?
Yes, simply use only M&M’s or increase the M&M amount. The texture will still be soft and chewy, just with fewer melty pockets of chocolate.
Christmas M&M cookie bars are exactly the kind of easy, festive bake that belongs in a holiday rotation. Once you’ve tested a batch, try different chocolate mixes, topping designs, or pan sizes and share the version that disappears fastest as your go-to Christmas bar recipe.