Preparation

1. 1. Preheat oven to 350ºF. Coat a 9-inch square baking pan with cooking spray; reserve.
2. 2. Prepare the crumb topping: Put all topping ingredients in a medium bowl and with your hands, mix, working in butter cubes until large clumps form. Reserve in refrigerator until ready to use.
3. 3. Prepare the cake: Put the flour, baking soda, cream of tartar and salt in a medium mixing bowl; whisk to combine. Put butter and granulated sugar in a large mixing bowl. Using a hand mixer, blend on medium-low speed for about 1 minute, until the mixture is light and fluffy. Add the eggs, one at a time, and mix until smooth. Scrape down the sides of the bowl and add vanilla. Mix until incorporated.
4. 4. Add half the dry ingredients and half the yogurt to the butter sugar mixture. Mix until blended, about 30 seconds. Scrape down the sides of the bowl and add remaining dry ingredients and yogurt. Mix about 30 seconds longer until smooth and all ingredients are blended.
5. 5. Pour batter into prepared pan and smooth the top. In a single layer, evenly arrange blueberries over the top of the cake and lightly press into the
   batter. Evenly spread crumb mixture all over top of blueberries.
6. 6. Bake for 55 to 60 minutes, or until crumb topping is evenly golden brown and tester comes out clean when inserted into the center of the pan. Remove from oven and place on a wire rack to cool. Cool completely before
   cutting.