Sparkling Berry Jam:1. Simmer sparkling wine, raspberries, strawberries, sugar, and salt over medium heat until sugar dissolves. 

Continue simmering, stirring occasionally, for about 15 to 20 minutes, until berries are broken up and fairly mushy (in a good way). If any scum appears on the surface, use a wooden or metal spoon to skim it off. 

Test for set-point by placing a teaspoon full of jam on a plate and placing the plate in the refrigerator for 15 minutes. If the jam has developed a skin and is holding together, take off the heat and cool. If not, continue cooking for another 10 minutes before testing for set-point again.

Cool completely before filling hamantaschen. Jam can be stored for up to 1 week in the refrigerator or frozen for up to 2 months.

Hamantaschen Dough:

Pulse sugar, butter, cream cheese, egg yolk, and vanilla In a food processor until combined. 

Add flour and pulse until dough forms a ball.

Turn dough out onto counter and knead a few turns until smooth and elastic. Flatten into a disk and wrap in plastic. Chill for at least 1 hour and up to 2 days, or freeze for 1 month.

Assembly:

Preheat oven to 350°F. Line a baking sheet with parchment.

Whisk egg and water together and set aside.

Roll out dough on lightly floured surface. Cut into 3-inch circles.

Spoon a small amount of jam into center of dough. Lightly brush edges with egg wash. Form into triangle, being sure to pinch edges tightly together.

Place on lined baking sheet. Continue with remaining dough.

Bake for 30 minutes or until golden brown.