Grease the bottom and sides of a 10-inch Spring form pan.Preheat oven to 350 and set the rack in the middle of the oven.Cream the butter and sugar. Beat in the eggs. Add yogurt and blend well. Add all of the dry ingredients to the bowl. Mix just until the wet and dry ingredients are incorporated. Fold in the berries. Spread the batter into the prepared pan (it will be thick).Prepare the streusel topping by mixing all of the ingredients together in a bowl. Sprinkle over the top of the cake, if making with streusel, otherwise, just bake the cake without a topping.Bake for 25-35 minutes, or until a toothpick inserted in the center of the cake comes out clean. Let cool for about 10 minutes, and run a knife around the sides of the Spring form before detaching the side form.When cake is completely cool, whisk powdered sugar in a bowl, add cream, salt and flavoring. Drizzle with a spoon over the cake. Let sit for about 30 minutes before cutting. Sprinkle with powdered sugar just before serving.