Preheat oven to 350° Fahrenheit.

Spray a 9-inch square baking pan with nonstick cooking spray. Place a piece of parchment paper over the bottom of the pan allowing it to extend up and over two of the sides by approximately 1 inch.

In a food processor, combine flour, sugar, lemon zest and salt and pulse until well blended.

Add butter pieces and pulse until butter breaks down to the size of peas and mixture looks like moist crumbles.

Pour the mixture into a bowl.

Place ¾ cup of the mixture into a separate bowl to be used later for the crumb topping. Press remaining shortbread crumbles evenly into the bottom of the prepared pan.

Bake crust for 12-14 minutes. It will not be brown. Cool slightly. Maintain oven temperature.

In a medium mixing bowl, whisk eggs, sugar, flour, yogurt and vanilla until well blended.

Pour the mixture evenly over the crust.

Place blackberries into a bowl and add jam. Using a large spoon gently combine jam with the berries. Do not overmix.

Spoon blackberry mixture over filling.

Scatter reserved crumbs evenly over the blackberry filling.

Bake for 50-55 minutes or until the top looks nice and brown and berries are bubbling.

Allow to cool completely.

Dust with confectioners’ sugar and cut into bars.

Serve with vanilla ice cream or whipped cream.