The dough for these bars is thick enough to hold the chocolate chips and M&M’s in place, so every slice gets a little of both. I like that there’s no need to portion individual cookies or keep rotating baking sheets; the dough goes into one 9×13-inch pan and bakes into a single slab that’s easy to cut and share.
Beating softened butter with both sugars gives the bars their cookie-like base, while the two kinds of chocolate bring different textures. Semisweet chips melt into the dough; the candy shells keep the M&M’s distinct. Once the edges are golden and the middle has set, you’ll have sturdy bars with soft centers and colorful bits throughout.
These M&M Chocolate Chip Cookie Bars are at their best when the pan has cooled and the chocolate has had time to settle into each cut.
Kitchen Note
Room-temperature eggs blend into creamed butter more smoothly than cold ones. I set them out before I start, so the mixture stays cohesive when each egg goes in.
Save these M&M Chocolate Chip Cookie Bars for an easy-to-slice bake packed with melted chocolate and colorful candy.
Why the 9×13-Inch Pan Matters for Evenly Baked Bars
Cookie bars depend on an even layer of dough. Spread the dough too thickly in the middle, and that part takes longer to set while the edges keep baking; uneven thickness can leave you with dark edges and a soft center. The 9×13-inch pan gives this batch room to bake as one consistent layer, so the edges and middle can finish close together.
That pan size also gives you a practical way to portion the batch into 24 bars. A smaller pan changes the thickness, so the same bake time won’t necessarily produce the same result. Rather than judging the bars by the clock alone, use the edges and center as your cues: the edges should be golden brown, and the center should look set. Those signs tell you more than color across the whole surface does.
What the Butter, Sugars, and Two Chocolates Each Bring
- Unsalted butter and sugars — Butter gives the bars their rich cookie texture, while light brown sugar brings moisture and a gentle molasses note. Granulated sugar helps the edges bake up with a little more structure. Softened butter creams properly; melted butter won’t give you the same starting texture. Dark brown sugar can stand in for light brown sugar if you want a deeper molasses taste, though the bars will taste a bit richer.
- Eggs — Eggs bind the dough and help the bars set into slices instead of crumbling. Large eggs are the right size for this balance; smaller eggs can leave the dough drier. Bring them to room temperature before mixing so they incorporate smoothly.
- Vanilla extract — Vanilla rounds out the butter and chocolate without taking over. A good-quality extract is noticeable in a simple cookie dough, but the standard grocery-store bottle works just fine here.
- All-purpose flour and baking soda — Flour gives the dough its structure, and baking soda helps the bars bake up rather than stay dense. Measure flour without packing it down; too much can make the bars dry and firm. For a gluten-free batch, use a measure-for-measure baking blend that includes xanthan gum, as described below.
- Semisweet chocolate chips and M&M’s — The chips soften and melt into the dough, while the candy shells hold their shape and add crunch. Semisweet chips balance the sweetness of the candy; a familiar grocery-store brand is fine. Keep the candies whole and fold them in gently so they stay distributed through the dough.
Mixing and Baking the Dough Without Overworking It
Cream the Butter and Sugars
Heat the oven to 350°F and grease a 9×13-inch baking pan. Beat the softened butter with the brown sugar and granulated sugar for about 2 minutes, until the mixture looks creamy and the sugars are worked through the butter. If the butter is cold and stiff, it won’t cream evenly; if it’s melted, the mixture won’t build the same texture. Start with butter that gives slightly when pressed but still holds its shape.
Add the Eggs One at a Time
Beat in one egg, let it blend into the butter mixture, and then add the second. Mix in the vanilla after the eggs are incorporated. The mixture should look cohesive rather than slick or separated. Scrape the bowl if butter is clinging to the sides so it gets mixed in evenly.
Mix in the Dry Ingredients Gently
In a separate bowl, whisk the flour, baking soda, and salt together before adding them to the butter mixture. Mix just until the dry ingredients disappear into the dough. Once flour is in, extended beating can make the bars tougher than you want. Stop when there are no visible dry patches.
Fold in the Chocolate and Bake
Stir in the chocolate chips and M&M’s, then press the dough into an even layer in the prepared pan. The dough is thick, so spread it all the way into the corners rather than leaving a mound in the center. Bake for 24 to 28 minutes, until the edges are golden brown and the center is set. Let the pan cool completely, about 1 hour, before cutting the bars.
Easy Ways to Change the Chocolate or Make a Gluten-Free Batch
Swap in White Chocolate Chips
Replace the semisweet chocolate chips with the same amount of white chocolate chips. The bars will taste sweeter and creamier, so this is a good choice if you want the candy pieces to be the main contrast.
Use Peanut Butter M&M’s
Replace the regular M&M’s with peanut butter M&M’s for a stronger peanut-butter note and a larger candy center in each bite. Fold them in gently, as you would the original candies.
Make Them Gluten-Free
Replace the all-purpose flour with the same amount of a measure-for-measure gluten-free baking blend that contains xanthan gum. The texture may be a little more delicate, so let the bars cool completely in the pan before slicing.
Storage and Reheating
- Refrigerator: Store the cut bars in an airtight container for up to 5 days. Chilling firms the chocolate and makes the bars less soft; let one sit at room temperature briefly before eating if you prefer a softer bite.
- Freezer: Freeze fully cooled bars in a single layer until firm, then transfer them to an airtight freezer container with parchment between layers. They keep well for up to 2 months; thaw at room temperature.
- Reheating: Warm an individual bar in the microwave for about 10 seconds to soften the chocolate. Longer heating can make the edges tough before the middle warms through.
Questions That Come Up When Baking These Cookie Bars
M&M Chocolate Chip Cookie Bars
Ingredients
Equipment
Method
- Heat the oven to 350°F.
- Grease a 9x13-inch baking pan.
- In a large bowl, beat the butter, brown sugar, and granulated sugar until creamy, about 2 minutes.
- Beat in the eggs one at a time.
- Mix in the vanilla extract.
- In a separate bowl, whisk together the flour, baking soda, and salt.
- Add the dry ingredients to the butter mixture and mix just until combined.
- Stir in the chocolate chips and M&M's.
- Press the dough evenly into the prepared pan.
- Bake for 24 to 28 minutes, until the edges are golden brown and the center is set.
- Cool completely in the pan, about 1 hour, before cutting into bars.
