Pastry:
1 cup all purpose flour
1 Tablespoon Sugar
1 pinch salt
6 Tablespoon Unsalted butter, cold
1 Egg yolk, slightly whisked
1 Tablespoon Lemon juice
Filling:
3 Tablespoon Cornstarch
1 Tablespoon Grand Marnier, or more if needed
3/4 cup Sugar
1 cup boysenberries or more as needed

Pastry:
In large bowl, stir together flour, sugar and salt. With pastry blender or food processor, cut in butter until it resembles tiny peas. Mix together egg yolk, lemon juice and 1 tablespoon water; sprinkle over flour mixture. Stirring with fork, add a little more water if necessary to hold dough together. Using hands, gently shape pastry into ball. Press dough 1/8″ thick into flan pan. Refrigerate while making filling.

Filling:
Preheat oven to 425°.
In small saucepan, stir together Grand Marnier & cornstarch till smooth. Stir in sugar. Add boysenberries and cook, stirring, over medium-low heat for 10-15 minutes or till thickened.

Let cool; spoon into shell, filling no more than 2/3 full. Bake in 425° oven for 10 minutes. Reduce heat to 350° and bake 15 minutes longer or till pastry is golden brown. Let cool 15 minutes before removing to rack.