Ingredients

2 cups all-purpose flour
3/4 cup white sugar
2 teaspoons baking powder
1/2 teaspoon salt
1/2 cup butter
1 egg
3/4 cup milk, or as needed
1 1/2 teaspoons vanilla extract

Streusel:
1 1/4 cup all-purpose flour

1 cup white sugar
1 cup brown sugar
1 1/2 TBSP ground cinnamon
1/2 cup butter

Directions

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9×9 inch pan. Make the streusel topping: In a medium bowl, combine all dry streusel ingredients. Cut in butter until mixture resembles coarse crumbs. Set aside.

In a large bowl, combine 2 cups flour, 3/4 cup sugar, baking powder and salt. Cut in butter until mixture resembles coarse crumbs. Crack an egg into a measuring cup and then fill add milk to make 1 cup. Stir in vanilla. Pour into crumb mixture and mix just until moistened. Spread half of the batter into prepared pan. Cover with streusel.  Spread the rest of the batter into the pan.  Sprinkle top with streusel.

Bake in the preheated oven for 45 to 60 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.