Preheat the oven to 350 degrees Fahrenheit.
Line a 13 x 9-inch pan with parchment paper. Parchment paper is essential for these sticky bars!Spread walnuts onto an ungreased cookie sheet.
Toast in the preheated oven for 10 minutes. Let them cool, then chop them coarsely.
In a mixing bowl, combine 1 cup (2 sticks) of room temperature butter, 2/3 cup brown sugar, and salt until the sugar is fully incorporated into the butter. Stir in 2 2/3 cups flour until the mixture starts to come together. Use your hands to mix until all the flour is incorporated.
Press the dough evenly into the parchment-lined pan and bake for 20 minutes.
Remove from the oven.
In a large bowl, whisk together eggs, light corn syrup, 1 cup brown sugar, molasses (if using), bourbon, vanilla, and 4 tablespoons melted butter.
Once thoroughly mixed, add the chopped, toasted walnuts.
Pour the walnut-corn syrup mixture over the baked shortbread base (no need to cool the base). Bake for 35-40 minutes until the topping is set and slightly browned around the edges.
Remove from the oven.Place chocolate chips in a large bowl.
Add 4 tablespoons of cubed butter.
Scald the heavy cream on the stovetop or in the microwave.
Pour the scalded cream over the chocolate and butter, mixing until smooth.
Pour the ganache over the baked walnut bars. Let cool for 30-60 minutes at room temperature.
Transfer the bars to the refrigerator to chill.
Cut into squares once completely chilled.