This festive bar has been my holiday shortcut for years: quick to throw together, insanely crowd-pleasing, and decorated in cheerful red and green so it instantly reads "party" the moment you pull it from the oven. I discovered this formula during a hectic December when I needed something that could be doubled, boxed, and delivered to neighbors without any drama. The first batch came out with crisp edges and a soft, chewy center and my kids declared them the official cookie for every school bake sale from then on.

What makes these bars special is their texture and the way the mix-ins stay glossy and colorful after baking. The dough is wetter than a traditional cookie dough, so you’ll press it into a foil-lined 9×13 pan for even baking and easy removal. Each bite balances buttery richness, deep caramel notes from packed brown sugar, and the playful crunch of M&Ms and jimmie-style sprinkles. These keep beautifully for a few days and are terrific warmed for a minute in the microwave. They’re my go-to when I need a lot of delicious cookies with minimal fuss.

Ingredients

• Unsalted butter (1/2 cup / 113 g): Use good quality block butter—Land O'Lakes or Plugrá give reliable flavor and melting behavior. Softened but not melted is ideal to avoid overly greasy dough.
• Packed brown sugar (2 cups / 400 g): Dark or light brown sugar both work; dark will add deeper molasses notes. Pack it firmly into the measuring cup for accurate sweetness and moisture.
• Large eggs (2): Bring to room temperature for best emulsification and rise; cold eggs can create streaks in the batter.
• Vanilla extract (1 teaspoon): Pure vanilla adds depth. If you have vanilla bean paste, use the same amount for flecks and extra aroma.
• Salt (1/2 teaspoon): Balances sweetness—use fine kosher or table salt. If using coarse sea salt, reduce slightly.
• Baking powder (1 teaspoon): Gives a gentle lift so the bars don’t become too dense—ensure it’s fresh for reliable results.
• All-purpose flour (2 cups / 248 g): Spoon and level into the cup to avoid packing; too much flour makes the bars cakier.
• Christmas M&Ms (1 cup): Or any seasonal candy-coated chocolate—gives color and a firm, sugary crunch.
• Christmas sprinkles (1/2 cup): Use jimmies (rod sprinkles) for best texture—nonpareils can bleed color more during mixing.

Instructions

Step 1 — Preheat and prep: Preheat the oven to 350°F. Line a 9×13-inch metal pan with heavy-duty foil and spray liberally with cooking spray—metal heats more evenly than glass here. The foil makes removal and slicing much cleaner; tuck the foil over the edges for easy lift-out after baking. Step 2 — Cream butter and sugar: In a stand mixer fitted with the paddle or with a hand mixer, beat the softened butter and packed brown sugar until the mixture is crumbly and slightly glossy, about 2–3 minutes. Scrape the bowl so everything is evenly mixed; this step dissolves sugar into the fat, giving a tender crumb. Step 3 — Add eggs and vanilla: Add the eggs one at a time, beating until the batter is smooth and homogenous. Stir in the vanilla. The batter will become more fluid—this is normal and helps produce the chewy center. Step 4 — Dry ingredients: Sift or whisk together salt, baking powder, and flour, then add to the batter in two additions. Mix on low speed until just combined; do not overmix or the gluten will tighten and the bars will be tough. Step 5 — Fold in mix-ins and press into pan: Stir in 1 cup M&Ms and 1/2 cup sprinkles until evenly distributed. The dough will be wet and tacky—spray your hands with cooking spray and press the dough into the prepared pan to an even layer. Sprinkle remaining M&Ms and sprinkles on top for a festive finish. Step 6 — Bake and cool: Bake 22–25 minutes until the edges have turned golden and the center is set but still slightly soft. Err on the side of underbaking—the bars will finish as they cool. Remove from oven and let cool completely in the pan on a wire rack before lifting the foil and slicing into bars.

Storage Tips

For the best texture, cool bars completely before storing. Keep them in a single layer or separated with parchment so the sprinkles don’t stick together. At room temperature in an airtight container they stay great for up to 4 days—beyond that, freeze flat in a sealed container for up to 1 month. To reheat, microwave an individual bar for 10–15 seconds for a freshly-baked feel, or warm a plate in the oven at 300°F for 5 minutes then place the bar on it to avoid sogginess from steam.

Ingredient Substitutions

If you need to swap ingredients: use margarine only if necessary (flavor and texture will be different). Brown sugar can be substituted with white sugar plus 1 tablespoon molasses per cup for the same moisture and caramel notes. For nutty interest, fold in 1/2 cup chopped toasted pecans in place of some M&Ms. Gluten-free all-purpose blends can replace flour 1:1 in many cases—expect a slightly different crumb. For dairy-free, use a firm vegan butter alternative and dairy-free chocolate candies, but results will be slightly less rich.

Serving Suggestions

Serve bars warm or at room temperature. Slice into 12 larger bars or 18 smaller squares for a cookie table. Pair with strong coffee, mulled cider, or a glass of cold milk. For a festive tray, stack bars on parchment and garnish with extra sprinkles and edible gold dust for holiday parties. They also travel well in cookie tins layered with parchment—ideal for gifting to teachers and neighbors.

Seasonal Adaptations

Switch mix-ins to match the season: pastel candies and white sprinkles for Easter, orange and black candies for Halloween, or peppermint chips and crushed candy cane in December for a cool mint twist. For autumn, fold in 1 teaspoon ground cinnamon and swap half the M&Ms for chopped toasted walnuts or pumpkin seeds to echo seasonal flavors.

Meal Prep Tips

Make two pans and freeze one unbaked by wrapping tightly in foil and plastic wrap; bake from frozen by adding 3–5 minutes to the bake time. For grab-and-go mornings, portion bars into individual sandwich bags and freeze—thaw next to your lunch or reheat briefly for a warm treat. Label containers with date and contents so you can rotate through holiday goodies with confidence.

These bars have been a centerpiece of holiday mornings and last-minute potlucks in my family—simple, forgiving, and always requested again. Make a double batch and hand out the extras; they’re reliable joy in a pan.