Preheat the oven to 350°F. Spray a 9x13x2-inch pan with nonstick cooking spray and set aside.
Whisk together 2 ¾ cups all-purpose flour, 2 ½ teaspoons baking powder, and ½ teaspoon salt in a medium bowl.
Add ⅔ cup melted unsalted butter and 2 ¼ cup packed brown sugar to a large bowl and mix until combined. Add 3 large eggs and 1 teaspoon vanilla extract, and mix until fully combined.
Add the flour mixture to the butter and sugar mixture and mix until combined. Stir in 2 cups milk chocolate chips and 1 cup chopped walnuts by hand.
Add the dough to the prepared pan and bake for 30-35 minutes, until the edges are golden brown. The center will still look underbaked, and it should! If it is baked any longer, the bars will become dry and crumbly.
Let the bars cool completely before slicing and serving.
Video
Notes
Storage Instructions
Room Temperature: Store in an airtight container for 3-4 days.
Refrigerator: Store in an airtight container for up to 7 days. Heat in the microwave for 5-10 seconds for a warm treat!
Freezer: Congo bars can also be frozen for up to 3 months. Leave at room temperature overnight to thaw.