Caramelise 100 g sugar in a pot. Deglaze with 800 ml warm water. Bring to the boil and simmer until the caramel dissolves again.
Cut 2 vanilla pods lengthwise and scrape out the pulp. Add the pulp and pods with 700 g sugar to the caramel. Simmer until the sugar is dissolved and the liquid is slightly syrupy.
Remove the vanilla pods from the syrup and place them in hot rinsed, e.g. twist-off bottles. Fill up with hot syrup and close tightly. Let the syrup steep for at least one day.