These monster cookie bars are soft, chewy and packed with peanut butter, oats, chocolate chips and M&Ms. This easy cookie bar recipe is quicker than making individual cookies and yields extra gooey, irresistible bars.
Post updated September 10, 2023: slightly revised recipe for chewier bars, new photos and tips.
If you want an easy, flavorful treat, these monster cookie bars deliver. They highlight peanut butter, chewy oats and plenty of chocolate candies. The peanut butter flavor is noticeable without overwhelming the bars, creating a balanced sweet-and-salty bite. Converting monster cookies into bars makes them faster to prepare and extra gooey.
Why choose cookie bars over drop cookies?
- They stay chewier and gooier.
- You can pack in more M&Ms and chocolate chips.
- No dough-chilling required.
- Faster and less messy than forming individual cookies.
Monster Cookie Bar Recipe
This recipe is straightforward and reliably delicious. Here’s a clear overview; follow the recipe below for exact measurements and times.
- Preheat the oven to 350°F (180°C). Line a 9×13-inch pan with parchment leaving a 1–2 inch overhang, or lightly grease the pan.
- In a large bowl, beat together 3/4 cup softened unsalted butter, 1 cup brown sugar and 1/2 cup granulated sugar with 3/4 cup smooth, commercially prepared peanut butter (avoid natural peanut butter where oil separates). Using both brown and granulated sugar helps produce a chewier bar.
- Mix in 2 large room-temperature eggs and 1 tablespoon vanilla extract until the mixture looks smooth and creamy.
- On low speed, add the dry ingredients: 1 2/3 cups all-purpose flour, 1 teaspoon baking soda and 1/4 teaspoon salt. Mix just until combined; too much flour can make the bars dry. The dough will be sticky.
- Stir in 1 1/2 cups old-fashioned rolled oats by hand for the best texture. Quick oats will work but give less chew; do not use instant or steel-cut oats.
- Fold in 3/4 cup chocolate chips and 3/4 cup M&Ms — cookie bars can handle a generous amount of mix-ins.
- Spoon the dough into the prepared pan and smooth into an even layer using an angled spatula or lightly greased fingers.
- Bake on the middle rack for 30–35 minutes, until the top looks set and the edges are slightly browned. Bake time depends on your oven and how gooey you like the bars.
Pro tip: For the gooey, warm texture shown in photos, slice the bars after about 40–45 minutes of cooling. For cleaner slices, cool completely before cutting. If you used parchment, lift the slab out using the overhang and cut on a board with a sharp knife.
Can I make these as individual monster cookies?
This formula is designed for bars. If you prefer drop cookies, follow a monster cookie cookie recipe developed for that format.
Can I freeze the bars?
Yes. Cool the bars completely, wrap tightly and freeze for up to 2 months. Thaw in the fridge and bring to room temperature before serving.
Equipment
- 9×13 inch (23 x 33 cm) baking pan
Ingredients
- 3/4 cup unsalted butter (168 g), softened
- 1 cup brown sugar (210 g)
- 1/2 cup granulated sugar (100 g)
- 3/4 cup smooth peanut butter (not natural)
- 2 large eggs
- 1 tablespoon vanilla extract
- 1 2/3 cups all-purpose flour (208 g)
- 1 teaspoon baking soda
- 1/4 teaspoon salt (omit if using salted butter)
- 1 1/2 cups old-fashioned rolled oats
- 3/4 cup chocolate chips (any variety)
- 3/4 cup M&Ms
Instructions
- Preheat oven to 350°F (180°C). Line a 9×13 pan with parchment or lightly grease.
- Beat butter, brown sugar, granulated sugar and peanut butter until smooth.
- Add eggs and vanilla; mix until creamy.
- On low speed, add flour, baking soda and salt until just combined.
- Stir in the oats by hand.
- Turn off the mixer and fold in chocolate chips and M&Ms.
- Spread the dough evenly in the prepared pan and smooth the top.
- Bake 30–35 minutes, until the top is golden and edges start to pull away. Cool at least 40 minutes before slicing for gooey bars, or cool fully for cleaner slices.
Notes
- Butter: If you use salted butter, omit the added salt in the recipe.
- Peanut butter: Use smooth, commercial peanut butter (not natural) for consistent results.
- Oats: Large rolled oats give the best texture. Avoid instant or steel-cut oats.
- M&Ms: Regular M&Ms work best; peanut M&Ms can make slicing more difficult.
- Storage: Store cooled bars in an airtight container at room temperature up to 4 days. Freeze cooled bars up to 2 months.
- Nutrition: Estimated per bar when sliced into 18 squares.
Nutrition (estimate per serving)
Calories: 359 kcal; Carbohydrates: 45 g; Protein: 6 g; Fat: 18 g; Sugar: 29 g.