Preheat oven to 350 degrees F, set rack in center of oven. Brush a 9x13-inch baking pan with butter.
Batter: In a medium size bowl, whisk together the flour, Clabber Girl Baking Powder, sugar and salt. In another bowl, whisk together the eggs, yogurt, melted butter and vanilla. Make a well in the center of the dry ingredients and lightly whisk in the egg and yogurt mixture. If it seems dry, stir in another tablespoon or two of yogurt.
In a separate bowl, toss the fruit with the lemon juice and zest. Spread half the batter in the prepared pan and top with half the fruit. Repeat with the remaining batter and fruit. Set aside to prepare the streusel.
Streusel Topping: Whisk together the flour, turbinado sugar, Clabber Girl Baking Powder, cinnamon, nutmeg and salt. Cut the butter in with your fingers or a pastry cutter. Gently stir in the egg and, using your hands, squeeze it into almond size chunks and toss over the fruit in the prepared pan.
Bake for 45 to 50 minutes - Rotate pan half way through baking. The fruit should be bubbly and the buckle should spring back when pressed gently in the center with your finger.
Best served warm. Keep covered at room temperature for up to 2 days or refrigerated and re-heated for up to 4 days.
* Turbinado or demerara will impart a nice crunch- white or brown sugar is also fine to use.
Yield: 8-10 servings