Preheat the oven to 350°F. Grease a 9" square pan.

To make the batter: 

Beat the butter and sugar until well combined in a large mixing bowl. Add the eggs, vanilla, and starter and mix until smooth. Make sure to scrape the bowl's sides and bottom.

In a medium bowl, whisk together the all-purpose flour, baking soda, salt, and baking powder. Add to the butter/starter mixture, stirring until evenly combined. Add the milk and mix until smooth.

To make the crumb topping: 

Whisk together the flour, sugar, cinnamon, and salt in a medium sized bowl. Add the vanilla extract to the melted butter. Stir to combine, then pour the butter into the flour mixture. Stir until you have a uniformly moist, crumb-like mixture.

Spread the batter in the prepared pan. Add the berries - do not mix. Finally sprinkle the crumb mixture evenly over the top.

Bake for 45 to 50 minutes, until a knife inserted in the center comes out clean, and the edge of the cake just barely pulls away from the pan. Remove it from the oven and cool on a rack.

Cake can be stored at room temperature in the pan covered with plastic for several days. Or you can wrap it well and freeze for longer storage.