Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 8-inch round cake pans.
In a measuring cup, combine milk, 1/2 cup orange juice, oil, beaten eggs, and 1 1/2 teaspoon orange zest. Set aside.
Sift flour, salt and baking powder into a large bowl. Mix in sugar. Make a well in the center and pour in the milk mixture. Stir until thoroughly combined.
Divide batter into prepared pans. Bake in the preheated oven for 35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
To make Orange Butter Frosting: Cream butter until smooth. Gradually beat in confectioners' sugar. Beat until light and fluffy. Beat in 2 tablespoons orange juice to bring to spreading consistency. Stir in vanilla and 1 teaspoon orange zest.