This batch of cookie bars has become my go-to treat for holiday baking. I first made them one December when I needed a quick, crowd-pleasing dessert for a last-minute office party. The bars came out chewy at the center, slightly golden at the edges, and studded with bright red and green candies that felt celebratory with every bite. They slice cleanly from a 9 by 13 inch metal pan and store beautifully, which is essential when you want to assemble cookie trays or send neighbors home with tasty portions.

What I love most is how forgiving the mixture is. The dough is wetter than typical drop cookie dough, which makes it easier to press evenly into the pan. I discovered a simple trick—spraying your hands lightly with cooking spray—so smoothing the surface takes seconds and saves time on cleanup. These bars are sweet, buttery, and rich, with playful crunch from the M&Ms and a soft, festive finish from jimmie sprinkles. They’ve become a holiday staple in my family, requested for cookie exchanges and school events.

Ingredients

• Unsalted butter: 1/2 cup (113 g) at room temperature. Use a high-quality block butter such as Plugr or Land O Lakes for a rich, reliable flavor. Room-temperature butter blends more evenly with sugar to create a tender crumb.
• Brown sugar: 2 cups packed (400 g). I use dark brown sugar for a deeper molasses note, but light brown sugar works fine. Packing the cup eliminates air pockets and ensures consistent sweetness and moisture.
• Large eggs: 2 eggs at room temperature. Room-temperature eggs incorporate better and give a silkier texture to the dough.
• Vanilla extract: 1 teaspoon. Pure vanilla extract is worth the modest extra cost; it brightens the overall flavor without being overpowering.
• Salt: 1/2 teaspoon. Balances the sweetness—use fine sea salt or table salt measured by volume.
• Baking powder: 1 teaspoon. Provides a subtle lift so the bars are soft but not cake-like.
• All-purpose flour: 2 cups (248 g). Spoon and level when measuring with cups for accuracy, or weigh for best results.
• Christmas M&Ms: 1 cup. Any colored chocolate candies will work; choose one with sturdy shells to avoid too much bleeding during mixing.
• Christmas sprinkles: 1/2 cup of jimmies. These hold shape better than nonpareils or sanding sugars when baked.
• Pan and finishing: A 9 by 13 inch metal pan lined with foil and nonstick spray for easy removal and clean slicing.

Instructions

Preheat the oven and prepare the pan: Set the oven to 350°F (177°C). Line a 9 by 13 inch metal pan with heavy-duty foil, allowing a small overhang on the long sides for easy removal later. Spray the foil thoroughly with cooking spray. Avoid glass pans because they alter baking time and can cause the edges to overbake. Cream butter and sugar: In a large bowl using a stand mixer or a hand mixer on medium speed, cream 1/2 cup softened butter with 2 cups packed brown sugar until the mixture looks crumbly and slightly glossy, about 1 to 2 minutes. Scrape down the bowl to ensure even mixing. The sugar does not need to be fully fluffy as you would for cookies; aim for smooth integration. Incorporate eggs and flavor: Add 2 room-temperature eggs one at a time, mixing briefly after each until combined. Stir in 1 teaspoon vanilla extract. The batter will loosen and become more glossy. Combine dry ingredients: Sift or whisk together 1/2 teaspoon salt, 1 teaspoon baking powder, and 2 cups all-purpose flour in a separate bowl. With the mixer on low speed, gradually add the dry mixture to the wet until just combined. The dough will be wetter and more cohesive than typical cookie dough—this is expected and produces a chewier bar. Fold in mix-ins and press: Gently fold in 1 cup of Christmas M&Ms and 1/2 cup jimmie sprinkles with a spatula until evenly distributed. Spray your hands lightly with cooking spray to prevent sticking and press the dough into the prepared pan, smoothing to an even layer. Reserve a few candies and sprinkles to scatter on top. Bake: Bake at 350°F for 22 to 25 minutes, rotating the pan halfway through if your oven runs hot. Look for the edges to turn a light golden brown while the center still appears slightly soft. Err on the side of underbaking; the bars will continue to set as they cool. Cool and slice: Allow the bars to cool in the pan on a wire rack for at least 30 minutes. Use the foil overhang to lift the slab from the pan, transfer to a cutting board, and slice into 12 even bars using a sharp knife. For cleaner cuts, chill briefly for 15 minutes before slicing.

Storage Tips

Store cooled bars in an airtight container at room temperature for up to four days. For longer storage, individually wrap bars in plastic wrap and freeze in a single layer before transferring to a freezer-safe bag; they’ll keep for up to one month. To thaw, move frozen bars to the refrigerator overnight or leave at room temperature for an hour. Reheat gently in a 300°F oven for 5 to 7 minutes to refresh the texture and soften chocolate centers.

Ingredient Substitutions

To make these dairy-free, substitute vegan stick butter or margarine of similar volume and use dairy-free chocolate candies. For a gluten-free option, use a 1-to-1 gluten-free flour blend and allow for a slightly longer rest time to hydrate the flour. If you prefer less sugar, reduce the brown sugar by 1/4 cup and add 1 tablespoon of molasses to keep the caramel notes. Nutty variations work well too—fold in 1/2 cup chopped toasted pecans in place of some candies.

Serving Suggestions

Serve bars at room temperature on a festive platter dusted with powdered sugar or alongside hot cocoa and coffee for a cozy dessert table. For gatherings, cut into smaller squares to create a mixed cookie tray. They pair nicely with whipped cream or a scoop of vanilla ice cream for a more indulgent dessert. Garnish with a few extra sprinkles or whole candies for a bright finishing touch.

Cultural Background

Sweet bars like these draw on the American tradition of pan cookies and blondies, which are essentially brown sugar–forward confections. The use of colorful candy and sprinkles for holiday presentation is a modern twist driven by festive marketing and the popularity of candy-coated chocolates. These treats combine the simplicity of classic pan-baked blondies with the playful nostalgia of childhood candies to create a very American holiday staple.

Seasonal Adaptations

Change the candy and sprinkle colors to fit different holidays—pink and red for Valentine’s Day, pastels for Easter, or orange and black for Halloween. Add warming spices such as 1/2 teaspoon cinnamon and a pinch of nutmeg for a winter variation, or fold in chopped dried fruit and white chocolate for a spring twist. For summer, try swapping M&Ms for chopped toasted almonds and shredded coconut for a lighter finish.

Meal Prep Tips

Make the dough up to one day ahead and keep it covered in the refrigerator. When ready to bake, bring to room temperature for 10 minutes, press into the pan, and bake as directed. To portion for lunches or gift boxes, wrap individual bars in parchment, tie with kitchen twine, and label with date. This makes them perfect for school treats, hostess gifts, or quick dessert add-ons.

These bars are simple, nostalgic, and endlessly adaptable. Whether you need a last-minute party contribution or a holiday project with the kids, they deliver consistent results and bright smiles. Give them a try and make them your own with candy combinations and finishing touches that reflect your celebration.