- 1 teaspoon lemon juice
- 1 cup milk
- 1/2 cup butter, softened
- 1 1/2 cups white sugar
- 1 egg, beaten
- 2 cups sifted all purpose flour
- 1/2 teaspoon salt
- 1 teaspoon baking soda
- 2 cups chopped fresh rhubarb
- 1 teaspoon vanilla extract
- Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch baking pan.
- Mix lemon juice with milk in a measuring cup and allow to stand for 5 minutes to sour. Beat butter and sugar in a bowl, using an electric mixer, until creamy, 2 to 3 minutes; beat in egg until well incorporated. Sift flour, salt, and baking soda together in a separate bowl. Mix dry ingredients into creamed mixture in several additions, alternating with soured milk. Gently fold rhubarb and vanilla extract into batter. Pour batter into prepared baking pan.
- Bake until top is lightly browned and a toothpick inserted into the center of the cake comes out clean, 45 to 50 minutes.