Preheat the oven to 375 degrees.
Grease a square baking pan or line it with parchment paper (or both).
Whisk the milk, oil, vanilla extract, and egg in a large mixing bowl until well combined.
In a separate bowl, combine the flour, sugar, baking powder, and salt.
Add the dry ingredients to the wet ingredients, stirring just until everything is combined.
Pour the coffee cake batter into the prepared pan and spread evenly.
In a bowl, combine the softened butter, brown sugar, flour, and cinnamon. Mix until the ingredients form a crumbly streusel mixture.
Sprinkle the crumb topping evenly over the batter.
Bake at 375 degrees for 25 minutes. Check the center for doneness with a toothpick or cake tester.
Allow the cake to cool slightly before slicing. Store cooled leftovers in an airtight container.