This batch of Christmas MM Cookie Bars has been my go-to holiday treat for years. I first developed the formula on a busy December afternoon when I wanted something faster and less fussy than rolling individual cookies, but just as crowd-pleasing. The result is a thick, chewy bar with a golden edge and a soft, slightly underbaked center that yields a satisfying bite every time. The colorful M&M’s add crunch and nostalgia, while the chocolate chips melt into pockets of gooey chocolate that make each slice feel indulgent.

I make these whenever we have family gatherings, school parties, or an impromptu cookie swap. One of my fondest memories is my niece insisting we bake them together while listening to holiday music; she scattered the red and green candies with fearless precision and declared them "the best cookie bars ever." These are forgiving to make, quick to assemble, and travel well — which means they show up on cookie platters and in lunchboxes across my neighborhood every December.

Ingredients

• All-purpose flour (2 cups): Use a reliable brand like King Arthur or Gold Medal. Measure by spooning into your cup and leveling with a knife for accurate volume. Flour provides structure; too much will make the bars cakey, so level carefully.
• Packed brown sugar (1 cup): Light brown gives a molasses hint and chew. Press firmly into the cup when measuring. Dark brown will make the flavor more caramel-forward if you prefer that.
• Granulated sugar (1/2 cup): Balances sweetness and helps with a crisp edge when combined with butter.
• Butter, softened (1 cup / 2 sticks): Use unsalted butter softened to room temperature (not melted). European-style butter adds richer flavor; if using salted, reduce added salt slightly.
• Baking soda (1 teaspoon): Gives a gentle lift and helps create lightness while maintaining chew.
• Salt (1/2 teaspoon): Enhances sweetness and balances flavors; if using salted butter, you can scale back to 1/4 teaspoon.
• Large eggs (2): Bring to room temperature so they emulsify with the butter and sugar for a glossy, uniform dough.
• Vanilla extract (1 teaspoon): Pure vanilla is worth it here; it rounds the flavors in the dough and enhances chocolate notes.
• Christmas M&M’s (1 cup): Use the festive red-and-green variety for color; reserve a few to press on top before baking for a decorative finish.
• Chocolate chips (1/2 cup): Semi-sweet works best for balance, but milk chocolate can make it sweeter and kid-friendly. Mini chips distribute more evenly; use what you have.

Instructions

Prepare the pan and oven: Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper leaving an overhang on two sides for easy lifting, or grease the pan well with butter. Proper pan preparation ensures the bars release cleanly and bake evenly. Cream butter and sugars: In a large bowl using a stand mixer fitted with the paddle or a hand mixer, beat the softened butter with the packed brown sugar and granulated sugar on medium speed until pale and fluffy, about 2 to 3 minutes. Scrape down the sides occasionally. This step incorporates air for a lighter crumb while the brown sugar keeps chewiness. Add eggs and vanilla: Add eggs one at a time, beating well after each addition, then mix in the vanilla. The mixture should look glossy and slightly thickened; under-mixing can yield streaks of flour later. Combine dry ingredients: Whisk together the all-purpose flour, baking soda, and salt in a separate bowl. Add the dry mix to the wet ingredients in two additions on low speed, mixing until just combined. Overmixing activates gluten and will make the bars tough, so stop as soon as you don’t see streaks of flour. Fold in chips and candies: Fold in 3/4 cup of the Christmas M&M’s and all of the chocolate chips with a spatula. Reserve the remaining candies to press on top. Folding gently preserves the texture and keeps the mix from turning too dense. Press into pan and top: Turn the dough into the prepared pan and press evenly to the edges using an offset spatula or your hands wrapped in plastic wrap. Scatter the reserved M&M’s over the top and press lightly so they stick into the surface but remain visible after baking. Bake and cool: Bake at 350°F for 20 to 25 minutes, rotating the pan halfway through. The center should look set but slightly soft; edges will be golden. Overbaking will dry the bars. Allow the pan to cool on a wire rack for at least 30 minutes, then lift out the parchment overhang and slice into 12 equal bars.

Storage Tips

Store cooled bars in an airtight container layered with parchment to prevent sticking. At room temperature they will stay fresh for about 3 days; refrigerate if you need to keep them longer — chilled bars firm up and slice cleaner. For freezing, cut into bars, flash-freeze them on a sheet pan until solid (about 1 hour), then stack with parchment between layers in a freezer-safe container for up to 3 months. Reheat briefly in a 300°F oven for 5 to 8 minutes or microwave a single bar for 10 to 15 seconds to revive the soft texture.

Ingredient Substitutions

If you’re out of Christmas M&M’s, substitute mini M&M’s, chopped chocolate-covered candies, or colorful sprinkles stirred in after baking for a decorative finish. To make them nutty, fold in 1/2 cup chopped toasted pecans or walnuts. For a richer bar, replace 1/4 cup of the flour with almond flour — note this will change texture slightly and make the bars denser. To reduce sweetness a touch, use 1/4 cup fewer chocolate chips or swap semi-sweet for bittersweet.

Serving Suggestions

Serve warm with a scoop of vanilla ice cream or simply dusted with a tiny snowfall of powdered sugar for holiday presentation. Pair with hot cocoa or coffee for an afternoon treat, or arrange on a platter with other holiday cookies for a festive spread. For gifting, stack three to four bars in a small box wrapped in wax paper and tied with ribbon — they look charming and travel well.

Cultural Background

Bars and slab-style confections are a practical evolution of classic drop cookies, designed for efficiency and portability. In many American kitchens, pan cookies became popular during the 20th century as families sought simple ways to produce abundant treats for gatherings. Decorating with colored candies is a nod to the visual traditions of holiday baking — an instantly joyful aesthetic that transcends generations.

Seasonal Adaptations

For winter variations, fold in 1/2 cup crushed peppermint candies for a mint-chocolate twist, or swirl 1/3 cup caramel sauce on top before baking and sprinkle with sea salt for a salted caramel variant. In summer, switch the M&M’s for dried cranberries and white chocolate chips to make a bright, seasonal bar.

Meal Prep Tips

Make the dough up to 48 hours ahead and keep it chilled in the fridge, then press and bake when ready — this shortens active holiday prep time. For large gatherings, double the batch and bake in two pans; the second pan can be started while the first is cooling. Use a sharp, warmed chef’s knife to slice for cleaner edges: run under hot water, dry, and slice between cuts.

These cookie bars are one of those small family traditions that grow into expected comforts — the kind of recipe you reach for when you want something reliably delicious and unfussy. Try them once and I suspect they’ll find a regular place on your holiday table.