Sour Cream-Rhubarb Squares

Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan. In a large mixing bowl, cream together the butter or margarine, shortening, and packed brown sugar until light and fluffy.

Beat in the egg until fully incorporated, then stir in the sour cream. In a separate bowl, whisk together the flour, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined and a smooth batter forms. Do not overmix.

Fold in the chopped rhubarb pieces evenly throughout the batter. Spread the batter uniformly into the prepared baking pan.

In a small bowl, combine the white sugar, cinnamon, and chopped nuts to create the topping. Sprinkle this mixture evenly over the surface of the batter.

Bake in the preheated oven for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown.

Remove the pan from the oven and allow the bars to cool completely in the pan on a wire rack before cutting into squares. Cut into desired bar sizes and serve.