Toast the chopped pecans in a dry skillet over medium heat for 3-4 minutes, stirring occasionally, until fragrant and lightly golden. This brings out their natural oils and deepens their flavor. While the pecans toast, dissolve the cornstarch in the evaporated milk, whisking until completely smooth with no lumps—this will help thicken the filling and create a silky texture.
In a medium saucepan, combine the butter, brown sugar, salt, and egg yolks over low heat. Whisk constantly to prevent the yolks from scrambling, allowing the sugar to dissolve and the mixture to become pale and slightly thickened, about 2-3 minutes. Pour in the cornstarch-milk mixture from Step 1 slowly while whisking continuously to incorporate it smoothly and prevent lumps. I find that patience here really pays off—rushing this step or using high heat can cause the custard to break or become grainy.
Continue cooking over low heat, stirring constantly for 7-10 minutes, until the mixture noticeably thickens and coats the back of a spoon. The mixture should go from thin and pourable to rich and pudding-like. Watch carefully—you want it thick enough to hold its shape slightly, but not so cooked that the edges begin to look overcooked or grainy.
Remove the saucepan from heat and let it cool for 1-2 minutes. Stir in the whiskey and vanilla extract, which will add a sophisticated, smoky depth to the dip. Fold in the toasted pecans from Step 1 and the chocolate chips, stirring until the chocolate is melted and distributed throughout. I like to use Ghirardelli semi-sweet chocolate because it melts beautifully without becoming oily, but any quality chocolate chips will work. The residual heat will melt everything together into a luxurious, chunky filling.
Transfer the mixture to a serving bowl and refrigerate for at least 2-3 hours until completely chilled and set to a spreadable consistency. The dip will firm up significantly as it cools. Serve alongside shortbread cookies for dipping, allowing guests to break off pieces and use the cookies to scoop up the rich, nutty filling.