Blueberry Crumb Coffee Cake

1 1/2 cups all-purpose flour 
¼ cup cornmeal
1 teaspoon baking powder
¼ teaspoon baking soda
¼ teaspoon salt
1 stick butter, softened
¾ cup granulated sugar or maple syrup
2 eggs
½ cup sour cream
1 1/2 teaspoons vanilla extract
2 cups (1 pint) blueberries

***Topping***
½ cup light brown sugar, packed
½ cup flour
½ cup quick oats
½ teaspoon ground cinnamon
dash ground nutmeg
5 tablespoons melted butter
½ cup finely chopped walnuts or pecans, optional

Grease a 9-inch springform pan. Heat oven to 350°.

Combine the 1 1/2 cups flour, baking powder, soda, and salt; set aside. In a mixing bowl cream the softened butter with the sugar. Beat in the eggs until smooth. Beat in sour cream and vanilla. With mixer on low speed, beat in the flour mixture just until blended. Spread the batter in the prepared baking pan. Sprinkle blueberries evenly over the batter.

In another bowl (or a food processor if you have one) combine the brown sugar, flour, oats, cinnamon, and nutmeg, stirring with a fork until smooth. Add the melted butter and blend well with the fork. Blend in chopped nuts, if using. Sprinkle the crumb mixture evenly over the blueberries.

Bake for 40 to 45 minutes, until the cake is firm and top is browned.

Let cool for about 10 minutes on a rack; remove the side of the pan and cool completely before slicing.