Preheat oven to 325. Spay a 13 x 9 in baking pan with cooking spray.
In a large bowl, mix together 2 1/2 cups of flour, baking powder, cinnamon, nutmeg, 1/2 tsp. salt, and 1 cup brown sugar. Add egg whites, buttermilk, vanilla, and blueberries and mix well. Spread batter in pan evenly. Bake for 25 minutes.
Combine flour, salt, brown sugar, and yogurt in a medium sized bowl and mix until crumbly.
After coffee cake has baked for 25 minutes remove from oven and sprinkle with crumb mixture. Return coffee cake to oven and bake for an additional 5 minutes. Cool cake before serving.