Preheat the oven to 350 °F (176 °C) and lightly grease a 9" (23 cm) tart pan with a removable bottom. Place a rimmed cookie sheet that's large enough for your tart pan on the rack in the lower-third section of your oven.

In a large mixing bowl using an electric hand mixer or stand mixer, beat the butter, sugar, salt and vanilla at medium speed until combined.

Gradually beat in the flour at low speed until the flour is well incorporated. Do not over mix!

Press the dough onto the bottom of the prepared pan and using a fork, poke holes about every 1".

Very carefully place the tart pan on the hot cookie sheet (this is catch any butter that may leak - which it shouldn't).

Bake for 15-20 minutes or until golden brown.

Meanwhile, place the chopped nuts on a baking sheet. When you remove the shortbread from the oven, toast the nuts for about 3-6 minutes, stirring after 3 minutes, or until they smell toasty (the time will depend on how finely the nuts are chopped).

Remove the shortbread from the oven and use a sharp knife to cut the shortbread into 8 wedges. The shortbread will be quite fragile so let it cool completely in the pan.

Carefully remove the cookies from the pan using a spatula.

Place a piece of parchment paper or wax paper on a baking sheet that will fit in your refrigerator.

Spoon the chocolate over the top and sides of a piece of shortbread and use the spoon to even it out. Place the shortbread on the parchment paper and sprinkle with nuts. Repeat with the remaining pieces.

Place in the refrigerator for about 30 minutes to allow the chocolate to harden. You could alternatively let the cookies sit at room temperature for about 2-3 hours or until the chocolate has hardened.

Store in an airtight container at room temperature for up to 3 days.