Make the Shortbread

1. Preheat your oven to 300 Fahrenheit, and grease and line the width of a large loaf pan (9.25 inches x 5.25 inches) with parchment paper.

   Tip: You can hold the parchment paper in place with metal binder clips over the rim of the loaf pan if you don’t want to trim it to fit.
   
   

2. In the bowl of a stand mixer fitted with the paddle attachment, add the softened unsalted butter (8 Tablespoons), powdered sugar (1/4 cup), granulated sugar (3 Tablespoons), vanilla extract (1 teaspoon), and kosher salt (1/2 teaspoon).
3. With the mixer on medium-high (level 4-6 on a KitchenAid mixer), cream the ingredients together until the color has lightened and the texture is fluffy and reminiscent of whipped frosting. Scrape down the bowl as needed to make sure everything has been creamed together evenly.
   
4. Add the all-purpose flour (1 + 3/4 cups – spooned and leveled, see Note*) to the mixing bowl and mix on low until the dough becomes a sandy texture and just starts to hold shape.
   
5. Add the dough to the prepared loaf pan and press into an even, dense layer with the back of a spoon.
   
6. Bake for 35-40 minutes, or until the edges are just starting to turn golden.
   While the shortbread bakes, make the cinnamon sugar spread so that it will be ready as soon as you pull the shortbread from the oven.
   
   

Make the Cinnamon Sugar Spread

1. In a small bowl, add the softened unsalted butter (4 Tablespoons), granulated sugar (1/4 cup + 2 Tablespoons), ground cinnamon (1+1/2 teaspoons), vanilla extract (1/2 teaspoon), and kosher salt (1/4 teaspoon).
2. Using a fork, mash and stir the ingredients together until a paste-like spread forms that is even in color.
   
3. Set aside and keep at room-temperature until you remove the shortbread from the oven.

Apply the Spread & Broil

1. Remove the shortbread from the oven when it is finished baking and change the oven temperature to “broil”.
2. Immediately spread the cinnamon sugar mixture evenly over the top of the baked shortbread (an offset spatula or the back of a spoon will make this easier). Be careful and use an oven mitt as the pan will be very hot, and work quickly so that the sugar crystals don’t melt. The butter will soften and become easier to spread as it warms.
   
3. Put the cinnamon-sugar-topped shortbread back in the oven for 2-3 minutes and remove when the cinnamon sugar spread is starting to bubble in the middle and has started to turn a darker caramelized shade of brown.

   Tip: DO NOT WALK AWAY DURING THIS STEP! It is very easy for things to burn when the oven is on broil, especially when working with sugar.
   
   

4. Carefully run a knife between the edge of the sugar layer and the edge of the pan, then allow to cool in the pan for 5 minutes.

   Tip: double-check that your oven is turned off, since broil is its hottest setting.

5. After 5 minutes, remove from the pan via the parchment paper tabs and, using a sharp chef’s knife or serrated knife, slice once lengthwise down the middle, and then into 8 even rows so that you have 16 evenly-sized mini-bars.

   Tip: it is easiest to cut the bars when they’re still warm, but not immediately after removing from the oven. If you wait until the bars are completely cooled to slice them, the topping will crack at the edges, and the shortbread will crumble, making it difficult to get evenly sized bars.
   
   

6. Allow to cool completely to room temperature before enjoying.