• See the recipe for the shortbread pastry. Bake the pastry in an 11-inch tart pan and let it cool. Keep the tart pan on a baking sheet to make it easy to move.
• Place the cornstarch in a small dish and stir in a splash of the evaporated milk until the cornstarch dissolves and there are no lumps. Pour in the rest of the milk while whisking and set aside.
• Place the butter, brown sugar, and salt in a saucepan over medium heat. After the butter melts, let the mixture come to a boil and cook stirring constantly for 2 minutes. 
• Give the milk/cornstarch mixture a quick stir then slowly pour it into the sugar mixture, whisking constantly. The mixture will bubble up toward the top of the saucepan but if you pour the milk slowly, it won’t overflow.  Simmer for an additional 2 minutes, stirring constantly.
• Remove the pan from the heat and add the butterscotch chips. Stir the butterscotch chips with a whisk until they are completely melted and the mixture is smooth. 
• Stir in the whiskey (if using), and vanilla extract. 
• Pour into the shortbread crust and place in the fridge for 6 to 8 hours to set up completely. 

Make the whipped cream topping

• Chill a mixing bowl in the freezer for 3 to 5 minutes then add the cold cream to the bowl. Add the sugar and vanilla.
• Whip on high speed with a whisk attachment until you see soft peaks form.
• Serve the butterscotch tart with the whipped cream.