Pre-heat oven to 180 degrees Celcius. Whisk the butter, salt and sugar until combined then add eggs one by one, mixing until light and creamy. Sift flour and baking powder together, combine with butter mixture and milk, whisk until smooth batter.

Pour batter into a 20 x 30 cm greased ovenproof dish. If you are using fresh apples, peel, core and slice. Do not add any sugar, cook apple slices until slightly softened. Layer apple slices on top of batter, bake for 40 minutes or until golden brown and cooked through. Run a knife around outside edge of tart, this will allow it to soak up more sauce.

Stir sauce ingredients over medium heat until smooth and mixture boils. Pour the sauce over the tart while it is still hot.