"This looks like a lot of ingredients and a lot of work, but it is pretty easy and they are so worth it! This has become our family favorite and most requested treat! Enjoy warm topped with ice cream."
Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Mix oats, 3/4 cup flour, brown sugar, baking soda, and 1/4 teaspoon salt together in a bowl. Stir 3/4 cup melted butter into oat mixture until evenly coated. Measure 3/4 cup oat mixture and reserve for later. Press remaining oat mixture into the prepared baking dish.
Bake in the preheated oven until lightly browned, about 5 minutes.
Combine white sugar, 1 cup melted butter, and vanilla extract in a bowl. Beat eggs, 1 at a time, into sugar mixture, mixing well after each addition, until thoroughly blended.
Sift 1 1/2 cups flour, cocoa powder, and 1 teaspoon salt together in a bowl; stir into sugar-egg mixture just until batter is blended. Fold chocolate chips into batter; pour over oat crust. Sprinkle reserved oat mixture over batter.
Bake in the preheated oven until a toothpick inserted in the center of the brownies comes out clean, 35 to 40 minutes.