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.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.

Press the dough evenly into the prepared baking dish. Bake for 25-30 minutes, or until the edges are lightly golden. Let cool completely in the pan on a wire rack.

Once cooled, prepare the topping. In a small saucepan, gently heat the whole milk and heavy whipping cream over medium-low heat until just simmering. Remove from heat and stir in the chocolate chips until melted and smooth. Let cool slightly for 10 minutes.