We have a mulberry tree in our backyard, and my husband has me make this every year.
Preheat oven to 375 degrees F (190 degrees C). Grease an 8x8-inch baking pan.
Beat milk, 1/2 cup white sugar, egg, and oil in a bowl. Add 1 cup flour, baking powder, and salt; mix until smooth. Pour into baking pan; sprinkle with mulberries.
Mix 3/4 cup flour, brown sugar, and 1/4 cup white sugar in a bowl; cut in butter and stir until mixture resembles crumbs, about 2 minutes. Sprinkle over cake.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 30 minutes.