½ cup unsalted butter, at room temperature
1 cup light brown sugar
½ cup creamy peanut butter
2 teaspoons vanilla extract
¾ cup all-purpose flour
1 teaspoon baking soda
1 teaspoon cornstarch
¼ teaspoon baking powder
¼ teaspoon salt
1½ cups old-fashioned oats
1 cup semisweet chocolate chips
1 cup M&M’s + additional for top of bars
- Preheat the oven to 350 degrees F. Grease a 9×13-inch baking pan and line with parchment paper so that it hangs over two sides.
- In a small bowl, whisk together the flour, baking soda, cornstarch, baking powder and salt.
- In a large bowl, cream together the butter, brown sugar, and peanut butter on medium speed until light and fluffy, about 3 minutes. Add the egg and vanilla, scraping down the sides of the bowl as needed. Reduce the mixer speed to low and slowly add the flour mixture to the wet ingredients and mix until just combined. Using a rubber spatula, stir in the oats, chocolate chips and M&M’s by hand.
- Turn the dough out into the prepared baking sheet and press/spread into an even layer. Press additional M&M’s onto the top of the dough. Bake for 15 to 17 minutes, until the edges are set and lightly browned and the top still looks slightly undercooked. Remove from the oven and cool completely before cutting into bars. The bars should be stored in an airtight container at room temperature for up to 4 days.