1 1/2 sticks unsalted butter, plus more for buttering the pan
1 1/2 cups all-purpose flour
1 teaspoon baking powder
1/2 teaspoon salt
1 cup light brown sugar
1/2 cup dark brown sugar
2 large eggs
1 1/2 teaspoons vanilla extract
1 cup milk chocolate chips
1/2 cup coarsely chopped walnuts
1/2 cup Semi-sweet chocolate morsels
Preheat the oven to 350 degrees F. Butter and line a 9-by-9-by-2-inch baking pan with parchment paper, allowing a 2-inch overhang. Butter the lining too.
Whisk together the flour, baking powder and salt in a medium bowl and set aside.
In a mixer, mix butter, sugars, vanilla extract, eggs.
Slowly add flour mixture and mix till fully incorporated.
Add nuts and chocolates.
Pour mixture into prepared pan.
Bake 25-30 minutes or until the top cracks slightly and is firm to the touch and a skewer inserted into the center comes out with moist pieces clinging to it.
Remove to a wire rack and let cool completely. Remove the bars from the pan using the parchment handles, transfer to a cutting board and cut into 2-inch squares.