Line an 8x8 inch baking dish with parchment paper and set aside. Preheat your oven to 325°F (163°C). In a large mixing bowl, combine 2 sticks of softened butter and beat with a hand mixer until light and fluffy. Add 1 teaspoon of vanilla extract and 1 ½ cups of powdered sugar, mixing until well combined.

Incorporate an egg into the mixture and beat again. Gradually add flour and salt, mixing until a dough forms. Set the dough aside. In a separate medium-sized mixing bowl, combine brown sugar, 2 tablespoons of cinnamon, 4 tablespoons of flour, 4 tablespoons of melted butter, and 1 tablespoon of vanilla extract. Stir until the mixture is well blended.

Divide half of the dough and press one half into the bottom of the prepared baking dish and flattening it evenly. If the dough is sticky, lightly oil your hands to make it easier to handle.

Pour the filling over the pressed dough, spreading it evenly. Next, place the remaining half of the dough on top and gently spread it out with oiled hands. Bake in the preheated oven for about 40 minutes, or until the center is no longer raw—check for doneness using the toothpick method.

Once baked, allow the bars to cool on the counter for 40 minutes. In a small bowl, mix 1 cup of powdered sugar, 2 teaspoons of cinnamon, and 3 teaspoons of vanilla until a smooth icing forms. Drizzle this icing over the cooled bars and spread it evenly.

Let the bars sit for 15 minutes to allow the icing to set slightly. (You can serve immediately for a gooey texture!) Lift the parchment paper to remove the bars from the dish and slice them into 8 small bars or 4 larger ones. Serve and enjoy!