M&M Cookie Bars: The Ultimate Soft and Chewy Crowd-Pleaser.

M&M Cookie Bars are a masterclass in texture and efficiency. Unlike individual cookies, which require multiple baking trays and precise scooping, these bars are baked in a single pan, resulting in a denser, fudgy consistency reminiscent of a blondie.¹ This format prevents the edges from drying out, ensuring every slice is as soft as the center of a traditional cookie.

The technical secret to these bars is the use of cornstarch and a high ratio of brown sugar.² The cornstarch softens the proteins in the flour, creating a “melt-in-your-mouth” crumb, while the molasses in the brown sugar provides a deep, toffee-like flavor and a chewy finish.³

Ingredients

The Cookie Dough

170g Unsalted Butter: Melted and slightly cooled.
150g Light Brown Sugar: Packed.
100g Granulated Sugar.
1 Large Egg + 1 Egg Yolk: (The extra yolk adds richness and structure).
2 Teaspoons Vanilla Extract.⁴
280g All-Purpose Flour.
1 Teaspoon Cornstarch.
1/2 Teaspoon Baking Soda.
1/2 Teaspoon Salt.

The Inclusions

180g M&Ms: (Milk chocolate or peanut butter work best).
100g Semi-Sweet Chocolate Chips: (Optional, for extra depth).

Instructions

1. Prep the Pan

Preheat your oven to 175°C. Grease a 20x20cm (8×8 inch) square baking pan and line it with parchment paper, leaving an overhang on the sides. This “sling” allows you to lift the entire block of bars out for clean slicing later.

2. Mix the Fats and Sugars

In a large bowl, whisk the melted butter with the brown sugar and granulated sugar. Because the butter is melted, it will naturally emulsify with the sugars, creating a smooth, glossy base that leads to a fudgy texture.

3. Incorporate Wet Ingredients

Add the egg, the extra egg yolk, and the vanilla extract. Whisk vigorously for 1 minute. You will notice the mixture becoming slightly paler and thicker as it aerates.

4. Fold in Dry Ingredients

Sift the flour, cornstarch, baking soda, and salt into the wet ingredients. Use a spatula to fold the mixture until just combined. Fold in about three-quarters of the M&Ms and chocolate chips.

5. Press and Decorate

Transfer the thick dough into the prepared pan. Use your hands or the back of a spoon to press it into an even layer. Scatter the remaining M&Ms and chocolate chips over the top, pressing them in lightly so they are visible after baking.

6. The Bake and Cool

Bake for 25 to 30 minutes. The edges should be golden brown, but the center should still look slightly “under-set.” Do not overbake, as they will firm up as they cool. Let the bars cool completely in the pan for at least 1 hour before lifting them out and slicing into squares.

Flavor & Texture Notes

The primary sensation is buttery, colorful crunch. The brown sugar and vanilla provide a nostalgic, bakery-style aroma, while the M&Ms offer a distinctive candy-shell snap that contrasts with the soft dough.

The texture is thick and fudgy, significantly more substantial than a standard cookie. The extra egg yolk ensures the bars remain moist and prevents them from becoming crumbly or cake-like.

Tips & Variations

The Holiday Swap: Use seasonal M&Ms (red and green for Christmas, or pastels for Easter) to theme these bars for any occasion.
Peanut Butter Twist: Swirl 60g of creamy peanut butter into the dough before baking for a “Monster Cookie” flavor profile.
Brown the Butter: For a sophisticated, nutty flavor, brown the butter in a saucepan before mixing it with the sugars.

Storage & Maintenance

Room Temperature: Store in an airtight container for up to 7 days. These bars stay soft for a long time due to the moisture in the brown sugar.
Freezing: These bars freeze exceptionally well. Wrap individual squares in plastic wrap and store in a freezer bag for up to 3 months.
Reheating: A 10-second pulse in the microwave will restore the molten chocolate center, making them taste like they are fresh from the oven.

FAQ

Can I use a 9×13 inch pan?

Yes, but you should double the recipe. If you use a larger pan with a single batch, the bars will be very thin and will likely bake in 15–18 minutes.

Why are my bars dry?

This is typically caused by over-baking or over-measuring the flour. Always scoop flour into your measuring cup with a spoon and level it off, rather than packing it down.

Can I use different candies?

Absolutely. Chopped Reese’s Cups, pretzels, or white chocolate chips all work well within this base dough.

Conclusion

M&M Cookie Bars are a reliable, high-yield dessert that simplifies the cookie-making process without sacrificing flavor or texture. By focusing on a “melted butter” method and incorporating cornstarch, you achieve a professional-grade chewiness that appeals to all ages.