Preheat the oven to 180°C/350°F and line a 20x20cm/9x9in cake pan with parchment paper.
In the bowl of a stand mixer fitted with a paddle attachment, cream together the butter and sugar until light and fluffy.
Add the flour, cornstarch and vanilla then mix until just combined.
Press the shortbread mixture into the prepared cake pan lined with parchment paper.
Flatten with a spatula or the bottom of a measuring cup.
Place in the preheated oven and bake for 20 minutes until a skewer comes out clean and the top is golden brown.
Remove from the oven and immediately slice into bars then allow to cool completely.
Once the shortbread is cool, melt the white chocolate then dip each shortbread cookie into the white chocolate and sprinkle over a little chopped pecan nuts.
Place the shortbread on a lined baking sheet and allow to cool and set before serving.