Bring the milk, cream, sugar and vanilla sugar to the boil, reduce the heat, reduce to approx. 400 ml. Remove the pan from the heat. Stir the gelatine into the hot liquid. Pour through a sieve into a measuring jug. Pour into four cold ramekins (each approx. 150 ml), cover and allow to set in the fridge for approx. 4 hrs.
Mix the strawberries with the sugar and liqueur, cover and leave to steep for approx. 30 mins.
Carefully slide the tip of a knife around the edges of the panna cotta. Briefly dip the ramekins in hot water and turn out the panna cotta onto plates. Top with the strawberries and sprinkle with the pistachios.