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.
Refrigerate the 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.
Add the pastry to the tin: Remove the dough from the fridge and add the dough to the greased tart tin. Use your fingers to press and push the dough outwards to line the bottom surface of the tin.
Ensure the pastry is pushed tight and snug into the bottom of the tin. You can also roll out the pastry to fit the tin then add it to the tin and use your fingers to spread it evenly.
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 heat. Stir continuous for 8 - 10 minutes to bring the caramel to a boil.
Don't be tempted to increase the heat as it may burn the caramel or cause it to become grainy. Once the caramel is bubbling across the whole pan, continue to stir for another 2 minutes then remove the saucepan from the heat immediately.
Add the caramel to the pastry: 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.