Blackberry Beauty Custard Flan

This flan should only be made several hours before it will be served.
It takes 1 1/2 hours to bake and then it needs another hour to cool.
It's one of those eat the same day you bake it desserts.
Simple to make, elegant to serve.

Ingredients for Crust:

• 1 cup flour
• 1/2 cup sugar
• 1 1/2 tsp baking powder
• 1 tsp lemon zest
• 1/2 cup cold butter
• 1 egg, slightly beaten

Filling Ingredients:

• 3 egg yolks
• 2 cups full fat sour cream
• 1/2 cup sugar
• 1/4 tsp vanilla
• 1/4 tsp lemon zest
• 1 egg white ( for coating the crust before adding berries and filling)
• 2 cups blackberries, plus more for garnish (if using frozen berries dust them with 1 tbsp of flour)
• whipping cream

Method for Crust:

1. Combine flour, sugar,  baking powder and zest. Cut in butter until fine crumbs form.
2. Stir in egg until mixture forms a dough.
3. Press into bottom and sides of 7"x11 flan pan with a removable bottom (or a 9" spring form pan.

Method for filling:

1. Mix together first 5 ingredients until just combined.
2. Froth the egg white with a fork and paint the bottom of the crust with it. 
3. Place the fresh or frozen blackberries over crust.
4. Pour the custard over the berries.
5. Bake in 325º oven for 1 1/2 hours. Cool.
6. Remove from pan. Slice and serve with whipped cream and more blackberries.