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M&M cookie bar squares on white parchment paper with center bar with bite taken out.

Soft M&M Cookie Bars

  • Author: Sally
  • Prep Time: 15 minutes
  • Cook Time: 27 minutes
  • Total Time: 1 hour, 40 minutes (includes slight cooling)
  • Yield: 24 bars
  • Category: Dessert
  • Method: Baking
  • Cuisine: American


Think of these bars as no-chilling, no-rolling EASY M&M cookies! Using melted butter, more brown sugar than white sugar, and a touch of cornstarch guarantee the absolute softest, chewiest M&M cookie bar texture.


  • 2 and 3/4 cups (343g) all-purpose flour (spooned and leveled)
  • 1 and 1/2 teaspoons cornstarch
  • 1 teaspoon baking soda
  • 1/2 teaspoon salt
  • 1 cup (226g) unsalted butter, melted & cooled for just 5 minutes*
  • 1 cup (200g) packed light or dark brown sugar
  • 1/2 cup (100g) granulated sugar
  • 2 large eggs, at room temperature
  • 2 teaspoons pure vanilla extract
  • 1 and 1/4 cups (about 260g) mini or regular-size M&Ms
  • 3/4 cup (135) semi-sweet chocolate chips


  1. Preheat the oven to 350°F (177°C). Adjust oven rack to the center rack position. Line the bottom and sides of a 9×13-inch metal or glass baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out of the pan. Set aside.
  2. Whisk the flour, cornstarch, baking soda, and salt together in a large bowl. Set aside.
  3. In a medium bowl, whisk the melted butter, brown sugar, and granulated sugar together until no brown sugar lumps remain. Whisk in the eggs and vanilla extract. Pour this into the flour mixture and mix together with a large spoon or rubber spatula. The dough will be very soft, slick, and thick. Fold in the M&Ms and chocolate chips. The M&Ms and chips may not stick to the dough because of the melted butter, but do your best to combine them.
  4. Transfer dough to the prepared baking pan and press/smooth into an even layer. Bake for 26–30 minutes or until lightly browned on the sides and top and a toothpick inserted in the center comes out mostly clean with a few moist (not wet) crumbs. Do not over-bake. If you notice the bars browning too much before 25 minutes, tent the pan with foil. Bars puff up in the oven, but settle as they cool.
  5. Allow the bars to cool in the pan set on a wire rack for at least an hour. While they’re still warm, I like to press a few more M&Ms and chocolate chips into the tops, just for looks (optional!). Once relatively cool, lift the bars out of the pan using the overhang on the sides and cut into squares.
  6. Cover leftover bars and store at room temperature for up to 1 week.


  1. Make Ahead & Freezing Instructions: You can make the cookie dough and chill it in the refrigerator for up to 3 days or freeze for up to 3 months. Allow to come to room temperature and continue with step 4. Baked and cooled cookie bars freeze well for up to 3 months. Thaw bars overnight in the refrigerator and bring to room temperature before serving.
  2. Special Tools (affiliate links): 9×13-inch Baking Pan or this one | Heavy-Duty Whisk 
  3. Cornstarch: If you don’t have cornstarch, you can leave it out. The cookie bars will still be soft.
  4. Butter: Avoid letting the melted butter cool for too long, otherwise your dough will be crumbly instead of soft (and your cookie bars can end up cakey). You want it still warm, but not hot enough to begin cooking the eggs.
  5. M&Ms: You can use regular-size, mini, or a mix of both. I like to crush some of them, too, to sprinkle on the top before baking. Totally optional!
  6. Do I have to add chocolate chips? You can skip the chocolate chips. If you skip them, increase M&Ms to 1 and 1/2 cups (about 300g). You could also replace the chocolate chips with white chocolate chips, butterscotch chips, or peanut butter chips.
  7. 9-Inch Square Pan: To make a smaller 9-inch pan of cookie bars, use this similar scaled-down recipe. For the add-ins, use 1 cup (200g) of M&Ms and 1/2 cup (90g) chocolate chips.

Keywords: M&M cookie bars