Mixed Berry Jam:

Hull strawberries (if using) and chop all berries into bite-size pieces.

In a small saucepan, combine chopped berries and sugar. Heat on the stovetop over medium heat, stirring occasionally, until berries have dissolved and mixture has thickened.

Do a test to make sure the jam mixture has reached thread stage. You can test using a candy thermometer (mixture should be approximately 105 degrees Celsius / 220 degrees Fahrenheit) or by spooning a small amount of mixture onto a plate, allowing it to cool slightly, then stretching the mixture between your thumb and forefinger. If a strand forms, thread stage has been achieved.

Once thread stage has been reached, pour the jam mixture onto a tray or silicone baking mat and allow to cool for a few minutes.

Once cool, transfer jam mixture to a small bowl. Stir in lemon juice, and set aside.

Pastries:

Preheat oven to 200° C / 400° F.

Line a baking sheet with parchment and set aside.

Unroll both sheets of puff pastry and slice each sheet into nine equal-size squares (or rectangles, depending on the shape of your puff pastry sheets). You should have eighteen squares total.

Place nine squares on the prepared parchment-lined sheet, allowing some space between each square.

Using a pastry brush, brush a small amount of egg wash around the border of each puff pastry square.

Place a spoonful of mixed berry jam into the center of each square. Be careful not to overfill the pastries, or to put the jam mixture too close to the edges of the square. This will prevent the jam from leaking during the baking process.

Place a second square of puff pastry over each jam-filled piece, and use your fingertips to gently seal the edges.

Egg wash the top of each pastry, then use a fork dipped in egg wash to crimp all edges.

Bake pastries for 18-20 minutes, or until golden brown. Allow to cool slightly before frosting.

Vanilla Bean Glaze:

In a small bowl, whisk together confectioner’s sugar, milk, vanilla bean paste, and food coloring (if using).

Spoon a small amount of vanilla bean glaze over the top of each pastry, and finish with sprinkles or colored sugar, if desired. Serve pastries warm or at room temperature.

Pastries are best enjoyed on the day they are made. Store leftovers in an airtight container at room temperature for up to one day.