dissolve sugar in 1/3 cup water in a saucepan on low heat. Increase heat to high, bring to boil and cook for 10-12 minutes, until mixture turns light toffee in colour. Add butter and stir until mixture comes together and pulls away from side of pan. Turn off heat and stir in half the cream. When bubbles subside, stir in remaining cream and salt flakes. Pour into pastry case. Bake for 12 minutes, until set. Cool completely.
To make the chocolate topping, melt chocolate and oil in a heatproof bowl set over a saucepan of simmering water, ensuring bowl does not touch the water, and stir until smooth. Spread chocolate over tart and refrigerate until set.