Preheat your oven to 375°F (190°C) and line a 9x13 inch baking pan with parchment paper.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, ¾ cup granulated sugar, 1 tablespoon baking powder, ½ teaspoon baking soda, and ½ teaspoon salt.

Cut in ½ cup of cold, cubed unsalted butter into the dry mixture until you achieve a coarse crumb texture.

Combine ¾ cup of buttermilk with 1 teaspoon of vanilla extract, then pour this mixture into the dry ingredients and stir until just combined.

Transfer the dough to the prepared baking pan and press it evenly across the bottom.

Mix together ½ cup brown sugar and 1 tablespoon ground cinnamon, drizzle 2 tablespoons of melted unsalted butter over the pressed dough, and sprinkle the cinnamon-sugar mixture on top.

Bake for 20-25 minutes until golden brown and a toothpick inserted in the center comes out clean.

Allow the bars to cool completely in the pan on a wire rack.

In a medium bowl, beat 4 ounces of softened cream cheese and ¼ cup softened unsalted butter until smooth. Gradually add 2 cups of powdered sugar and 1 tablespoon of milk.

Spread the cream cheese frosting over the cooled bars and cut into squares or rectangles for serving.