Step 1

Preheat oven to 350°F. Grease an 8-inch square pan.

Step 2

In a large bowl, beat the butter and brown sugar until well-combined. Beat in the eggs.

Step 3

In a medium bowl, sift together the flour, salt and baking powder. Gradually beat the dry ingredients into the butter and brown sugar mixture.

Step 4

Add the orange juice, milk, vanilla and orange zest and beat until well-combined.

Step 5

Pour cake mix into prepared pan and sprinkle with streusel topping. Bake for 45 minutes or until the top is golden brown. Allow to cool completely in the pan set on a wire rack.

Step 6

In a medium bowl, stir together the sugar, flour and orange zest.

Step 7

Add the butter to the bowl. Use your fingers to pinch the butter into the flour mixture until crumbly in texture. Alternately, you can use a fork or pastry cutter to mix the ingredients.