• Preheat the oven to 350°F. Line a 9-inch square baking dish with parchment paper, allowing the paper to hang over two sides.
• To a large bowl, add butter and sugar. Using a hand mixer on medium speed, cream together the butter and sugar until light and fluffy.
• Add the egg yolks and vanilla. Mix until combined.
• In a separate bowl whisk together the flour, cinnamon, and salt.
• Slowly add the flour mixture to the butter mixture. Mix on low until combined, scraping down the sides of the bowl as needed.
• Working 1 tablespoon at a time, add milk until the mixture is sticky, thick, and well combined.
• Press the dough into the bottom of the baking dish. Pierce the dough with a fork in one-inch intervals.
• Bake for 35-40 minutes, or until the top is golden brown.
• Remove the shortbread from the oven. While the crust is still hot, press it down with a spatula and set it aside to cool while you prepare the chocolate ganache.

Whipped Ganache

• Put the metal bowl and whisk attachment from your stand mixer into the refrigerator to chill while you make the ganache.
• To a microwave-safe bowl, add heavy whipping cream. Heat the whipping cream in the microwave for about 2 minutes. The cream should be just boiling.
• Carefully pour the chocolate morsels into the cream. (It may rise up and bubble and this is okay.)
• Let sit for 5-10 minutes. Then, whisk the chocolate and cream until shiny and smooth, about 1 minute.
• Pour the ganache into your chilled bowl and whip on low, gradually increasing to medium speed. It will lighten in color and increase in volume as you whip.
• Spread whipped ganache across the top of the cooled bars with an offset spatula. Cut and serve.