Blackberry Kuchen

From 6 Bittersweets
Adapted from Better Homes and Gardens: New Baking Book via How To Eat A Cupcake
Makes 1 9-inch cake (up to 12 servings)

XIAOLU'S NOTES: I think any berries or cherries or even peaches would work well in place of the blackberries. Though the directions say not to grease the pan, I lined the base in parchment and might lightly grease the sides next time to ensure a clean release.

1 cup all-purpose flour
1/2 cup sugar
1/8 tsp salt
1 tsp baking powder
1/4 cup butter, melted
2 large egg whites (save the yolks for the filling)
1 tsp pure vanilla extract

2 cups fresh or frozen blackberries or raspberries (I used frozen blackberries)

Filling
2 large egg yolks (saved from egg whites used for base)
1 large egg
2 Tbsp all-purpose flour
1/2 cup sugar
1 1/2 cups plain low-fat yogurt [use Greek yogurt for a firmer custard]
1 1/2 tsp lemon zest (from about 1/2 a lemon)
a pinch of salt
1 tsp pure vanilla extract
1/4 tsp almond extract

Preheat the oven to 350 degrees F. If using frozen berries, thaw at room temperature 15 minutes; drain.

For the filling, place egg and yolks in a large mixing bowl then mix well.  Sprinkle with 2 tablespoons flour and stir again until smooth. Add 1/2 cup sugar, yogurt, lemon zest, salt, and vanilla and almond extracts. Mix until evenly incorporated; set aside.

In a medium mixing bowl, sift together 1 cup flour, 1/2 cup sugar, salt, and baking powder. Add butter, egg whites, and 1 teaspoon vanilla. Gently stir everything together by hand until mixed well. (Mixture will be like soft cookie dough.) Spread onto the bottom of an ungreased 9-inch springform pan; sprinkle berries on top. Pour the filling prepared earlier over the berries.

Bake the kuchen for about 55 minutes or until center appears set (slightly wobbly) when shaken gently. Cool in the pan on a wire rack for 15 minutes; undo the clasp on the side of the pan and remove the ring. Cover the kuchen and chill it in refrigerator for 4 to 24 hours.

To serve, remove the pan bottom. Transfer to a platter.