Preheat the oven to 200 degrees C / Gas 6. Lightly grease a large baking tray.
Salted caramel sauce:
Place 150g sugar in a saucepan over low heat; cook, without stirring, until it starts to turn golden brown in colour.
Heat 200ml of single cream in the microwave for 10 seconds. Add the warm cream, 80g butter and salt to the caramel, stirring constantly. Continue to cook for 2 minutes until smooth. Set aside to cool at room temperature.
Heat milk, water, sugar and butter in a saucepan over medium heat until it starts to boil; remove from heat and beat in flour with a wooden spoon until the dough starts to come off the sides of the pan. Add one egg and mix. Add the second egg and mix until smooth.
Use 2 tablespoons to drop 12 buns onto the baking tray. Bake for thirty minutes in preheated oven, then turn the oven off but don't open the door; allow the choux buns to continue to cook for 10 minutes or until golden brown. Remove the buns from the oven; transfer to a cooling tray and allow to cool completely.
To fill the buns; make a small hole in the side of each bun with the tip of a nozzle; pipe whipped cream or creme patissiere into the hole.
Individual servings: Place one choux bun flat side up on a dessert plate; spoon 1 teaspoon of caramel sauce on top and sandwich with another choux bun. Drizzle caramel sauce on top and decorate the edge of the plate with dots of caramel before serving.