Make the sweet pastry: For the sweet pastry, sift the plain flour, icing sugar and salt into a mixing bowl. Add the butter and use your fingers to rub the butter into the mixture until it resembles breadcrumbs. Add the vanilla extract and milk and use a spoon to mix the ingredients together to help form a dough. Once the mixture begins to come together, use your hands to form a smooth dough. Shape the dough into a disc and then wrap in cling film and refrigerate for 1 hour. While the pastry is in the refrigerator, grease a loose bottom tart tin which measures approximately 25cm in diameter and set aside.
Remove the dough from the fridge and add the dough to the greased tart tin to line the tin with the pastry. Press the pastry into tin also concentrating on the corners and use your fingers to ensure that the pastry is pushed tight and snug into the tin. You can also roll out the pastry to fit the tin if you prefer. Prick the base of the pastry case all over with a fork and refrigerate the pastry in the tin while you preheat the oven to gas mark 4/350oF/180oC/160oC fan.
Bake the pastry: Place the tart tin on a baking tray and bake for 20 - 25 minutes or until the pastry is lightly golden in colour. Remove from the oven and leave to cool while you make the caramel topping.
Make the caramel: Add the condensed milk, butter and light brown sugar to a small heavy-duty saucepan then place the saucepan over a low - medium heat. Stir continuous and bring the caramel to a boil. Once the caramel begins to bubble, stir for another 2 minutes then remove the saucepan from the heat immediately. Pour the hot caramel onto the pastry. Use a palette knife or spoon to spread the caramel evenly on the pastry. After 5 minutes, sprinkle with chocolate sprinkles and allow to set at room temperature for 1 hour before cutting.