Thanks to purchased puff pastry, these turnovers are easier than they look. Yossy's jam recipe makes a bit more than you'll need for the mini turnovers, but it's great on toast.
For jam: Combine berries, granulated sugar, lemon juice, and cardamom in a large saucepan. Bring to boiling over medium-high, using a fork to mash berries. Reduce heat to medium and cook 20 to 25 minutes or until very thick, stirring frequently. Transfer jam to a heat-safe container. Stir in vanilla. Let cool slightly. Chill until cooled.
Preheat oven to 425ºF. Line two baking sheets with parchment paper. For egg wash: Whisk together egg and 1 teaspoon water.
Dust a work surface with flour and roll one sheet of the puff pastry to a 12-inch square. Cut into sixteen 3-inch squares. Brush edges with egg wash and top with a teaspoon of jam. Fold a corner over to make triangle; press edges with a fork to seal. Transfer to baking sheet. Repeat with remaining puff pastry squares.
Brush turnovers with remaining egg wash and prick a few times. Bake about 12 minutes or until deep golden brown and puffed. Transfer to a wire rack. Repeat with remaining pastry; you will have extra jam.
Meanwhile for glaze: Combine confectioners sugar, 1 Tablespoon of the remaining jam, 2 teaspoons lemon juice, and a pinch of salt in a small bowl. Whisk until smooth, adding more lemon juice as necessary to make smooth. Drizzle over turnovers. Makes 32 turnovers.
To store: Chill turnovers in an airtight container up to 2 days or freeze up to 1 month; thaw before serving. Store extra jam in the refrigerator in an airtight container up to 1 week.