Preheat your oven to 350°F (175°C) and line a 9x13-inch baking sheet with parchment paper, leaving some overhang for easy removal later.

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Stir in the vanilla extract. Gradually add the flour and salt, mixing until just combined. The dough will be crumbly but should hold together when pressed.

Transfer the shortbread dough into the prepared baking sheet. Use your hands or a spatula to press it evenly into the bottom of the pan, smoothing it out into an even layer.

Bake in the preheated oven for 20-25 minutes, or until the edges are lightly golden. Remove from the oven and let it cool in the pan for about 10 minutes.

While the shortbread is cooling, melt the chocolate chips in a microwave-safe bowl. Heat in 15-second intervals, stirring in between, until completely melted and smooth.

Once the shortbread has cooled slightly, pour the melted chocolate over the top, spreading it evenly with a spatula to cover the entire surface. Top with walnuts, or the toppings of your choice.

Allow the chocolate topping to set at room temperature for about 30 minutes. For quicker results, you can place it in the refrigerator for about 15-20 minutes.

Once the chocolate has fully set, lift the shortbread and chocolate out of the pan using the parchment paper overhang. Place it on a cutting board and cut into squares or bars.