Pour 4 tbsp agar. water and leave to swell. Prepare parchment paper on which to place the marshmallows. Tip: if you use thick apple jam, it is better to first stir it to a more liquid consistency.
Prepare the syrup. Place the pan with the sugar and the remaining water over medium heat, and after boiling, cook for another 5-7 minutes. Do not stir the syrup with a spoon yet, just shake the pan slightly. Then add citric acid, stir with a spoon, pour in the agar and cook for another 3-5 minutes until thickened.
Prepare the marshmallow mixture. In a separate bowl, thoroughly mix the jam, vanilla and egg white until the mixture turns white and becomes several times larger. Then, without stopping whisking, pour in the syrup in a thin stream, and when it runs out, beat for about another minute.
Leave the marshmallows to harden. Quickly transfer the marshmallow mixture into a piping bag and begin pipetting onto the parchment paper. Then let the marshmallows sit until the outside is covered with a thin crust.
Before serving, mold the marshmallow halves together and roll in powdered sugar.