Line a 9x13-inch metal baking pan with parchment paper. Set aside.
In a large mixing bowl, cream together 2 cups salted butter, 1 cup granulated sugar, 1 tablespoon vanilla bean paste, and ½ teaspoon salt for 2 minutes, scraping down the sides of the bowl about halfway through.
In a separate, large mixing bowl, whisk together 5 cups all-purpose flour, ⅓ cup powdered sugar, 2 tablespoons cornstarch, and ½ teaspoon salt.
Add the flour mixture to the butter mixture in 3 parts, mixing between each addition just until incorporated. The dough will be mixed but slightly crumbly.
Transfer about ⅔ of the dough to the prepared baking pan and press it evenly into the bottom of the pan.
In a medium bowl, mix together 1¼ cup dark brown sugar, ½ cup salted butter, 2 tablespoons ground cinnamon, 2 tablespoons cornstarch, 2 teaspoons vanilla extract , and ¼ teaspoon salt until fully combined.
Spread the cinnamon roll filling mixture out over the top of the shortbread dough, but don't spread it all the way to the edge; leave a border of about ¼ inch.
Top with the remaining shortbread dough and gently press to cover; some gaps are perfectly fine!
Chill the shortbread in the refrigerator for 30 minutes.
With 15 minutes left of chilling, preheat the oven to 325°F.
After chilling, bake for 40 to 45 minutes until the tops and edges of the shortbread should be just turning golden brown.
Transfer the pan to a wire rack to cool.
Let the shortbread cool completely before lifting it out of the pan. Then use a sharp knife to cut the shortbread into squares.
In a small bowl, whisk together 1 cup powdered sugar, 2 tablespoons heavy cream, 1and 1 tablespoon vanilla bean paste to create the icing.
Drizzle the icing over the sliced shortbread bars and let set.