Preheat the oven: Start by preheating your oven to 350°F (175°C). Grease a 9x9-inch baking pan with cooking spray or butter, ensuring the bars won’t stick.
Create the crust: In a mixing bowl, combine 1 ½ cups graham cracker crumbs, 5 tablespoons melted unsalted butter, and 1 tablespoon granulated sugar. Mix until the crumbs are fully coated and the mixture resembles wet sand. Press this mixture evenly into the bottom of the greased pan to form a firm crust.
Add the chocolate and nuts: Evenly scatter 1 cup chocolate chips and 1 cup chopped pecans over the crust, creating a deliciously decadent layer. Be generous with the toppings to ensure every bite is filled with chocolate and nuts.
Mix the condensed milk: In a separate bowl, combine 1 cup sweetened condensed milk and 1 teaspoon vanilla extract. Stir well until fully incorporated.
Pour and bake: Pour the condensed milk mixture evenly over the layers in the pan. Spread it slightly with a spatula to ensure an even coverage. Place the pan in the preheated oven and bake for 25-30 minutes, or until the edges are bubbly and golden brown.
Cool and serve: Once baked, remove the pan from the oven and let it cool for at least 30 minutes. This cooling time allows the bars to set properly. After they cool, cut them into squares and enjoy!