Preheat an oven to 375°F. Grease and flour a 9-inch cake pan. Set aside.
Whisk together flour, sugar, baking powder, salt, and orange zest. Add the milk, orange juice, oil, egg, and vanilla extract. Stir just until combined. Pour into the prepared pan.
In a small bowl, combine the topping ingredients using a pastry blender or 2 crisscrossed knives until the mixture is the texture of cornmeal. Evenly sprinkle the mixture over the cake batter.
Bake for 40-45 minutes, or until a toothpick inserted near the center tests clean.
Remove from the oven and allow the coffee cake to cool completely in the pan.
Notes
How long is coffee cake good for?
Covered and stored in the refrigerator, it will last about 5-7 days. Covered and stored at room temperature, you'll need to use it within 1-2 days.
How to store coffee cake?
The best way to store this recipe is by covering it with aluminum foil, plastic wrap, or by placing it in an airtight container.
Can you freeze coffee cake?
For best quality, allow the coffee cake to cool completely and then wrap it tightly in plastic wrap, aluminum foil, zip-top bag, or freezer-safe container. It needs to be used within 3 months. Unwrap and allow to thaw at room temperature when you're ready to eat it.