Monster cookie bars in a 9×13 pan combine 1 cup of peanut butter, 1/2 cup of butter, 1 1/4 cups of sugar, 2 eggs, 2 cups of oats and 1 cup of flour with 1 cup each of candy-coated chocolates and chocolate chips. Press the dough into the pan and bake at 350°F for 20 to 25 minutes for thick, chewy bars.
They have everything in a monster cookie (peanut butter, oats and two kinds of chocolate) without scooping a single ball of dough.
Why a 9×13 Pan Is Right for Monster Cookie Bars
This dough makes about 6 cups, which spreads to a layer a little over 1/2 inch thick in a 9×13 and rises to roughly 1 inch. That thickness keeps the center chewy while the edges set. Monster cookie dough is heavy with oats and add-ins, so it bakes more evenly in a pan than as large drop cookies, which tend to brown at the edges before the middle is done.
Ingredients for 9×13 Monster Cookie Bars
- 1/2 cup (1 stick) unsalted butter, softened
- 1 cup creamy peanut butter (regular, not natural)
- 3/4 cup packed brown sugar
- 1/2 cup granulated sugar
- 2 large eggs
- 2 teaspoons vanilla extract
- 1 cup all-purpose flour
- 1 teaspoon baking soda
- 1/2 teaspoon salt
- 2 cups old-fashioned rolled oats
- 1 cup candy-coated chocolate pieces, plus a handful for the top
- 1 cup semisweet chocolate chips
How to Make Monster Cookie Bars in a 9×13 Pan
- Heat the oven to 350°F. Line a 9×13 pan with parchment or grease it well.
- Cream the fats and sugars. Beat the butter, peanut butter, brown sugar and granulated sugar until fluffy, about 2 minutes.
- Add the eggs and vanilla and beat until smooth.
- Add the dry ingredients. Mix in the flour, baking soda and salt on low, then the oats.
- Stir in the candies and chips. The dough will be thick.
- Press into the pan with damp hands or a spatula, then press the extra candies into the top.
- Bake 20 to 25 minutes, until the edges are golden and the center looks just set. A toothpick should come out with a few moist crumbs.
- Cool at least 1 hour in the pan before cutting into 24 bars.
Cook and Prep Times
- Prep: 15 minutes
- Bake: 20 to 25 minutes at 350°F
- Cool: 1 hour
- Makes: about 2 dozen bars
Tips for Chewy, Not Dry, Bars
- Pull the pan while the center still looks slightly soft. Oat bars dry out quickly with extra minutes.
- Use regular creamy peanut butter. Natural peanut butter separates and makes the bars greasy and crumbly.
- Old-fashioned oats give the most chew; quick oats work but make a softer, more cake-like bar.
Changing the Pan Size
- 8×8 pan: halve the recipe (use 1 egg) and bake 18 to 22 minutes.
- Half sheet pan: double the recipe and bake 20 to 25 minutes; the bars are thinner.
- Cookies instead: scoop 2-tablespoon balls and bake 10 to 12 minutes.
Storage
Keep the bars in an airtight container at room temperature for up to 4 days, or freeze them for up to 3 months. A slice of bread in the container helps keep them soft.
Frequently Asked Questions
Are monster cookie bars gluten-free?
Not as written, because of the flour. For a gluten-free version, use certified gluten-free oats and a 1-to-1 gluten-free flour blend, and check the labels on your candies and chips.
Can I use crunchy peanut butter?
Yes. It adds texture and works the same way in the recipe.
Can I swap the add-ins?
Keep the total at about 2 cups. Butterscotch chips, peanut butter chips, raisins or chopped peanuts all work.
For another bar made in a square pan, see our pecan pie bars in an 8×8 pan.
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